Windows

1. Reboot your computer and try the CD/DVD player again. Sometimes the problem can be resolved by doing this.
2. Purchase a CD cleaner for your CD/DVD drive, such as Fellowes CD/DVD Drive Lens Cleaner. It can remove oxide residue, dust and debris from the laser lens and may correct the problems causing an I/O error.

3. Try the CD in another computer if you have access to one just to see if it's the CD rather than the computer that is causing the problem. If you don't have access to another computer, try a different CD and see if you get the same error.
4. Alter the transfer mode on your CD/DVD drive. You can do this by going to the 'Start' menu, and then right-clicking on 'My Computer' and selecting 'Manage.' In the resulting window select 'Device Manager.' You should then notice in the right pane 'IDE ATA/ATAPI' controllers, you want to expand this by clicking on it, then right-click your CD/DVD drive and select 'Properties.' Next click on 'Advanced Settings.' At this point you should notice a transfer node box that signifies your CD/DVD drive; usually this is 'Device 1.' Finally, open the drop down menu and select 'PIO,' then click 'Ok' and exit.
5. Check to make sure all devices that are hooked up to your computer are turned on. For example, if you have an HP printer attached to your computer and it is turned off, this can cause an I/O error to pop up. As soon as you turn it back on, the I/O error should disappear the next time you reboot.
6. Download and run a registry cleaner on your computer. Often if Steps 1 through 5 don't correct the problem, cleaning your registry can.

1. Perform a file search for the 'msdatgrd.ocx' file on your computer's hard drive. Look in the 'C:\Winnt\system32' or 'C:\Windows\system32' folders since most system files are stored there.
2. Copy the file from another computer running the same operating system and service pack installation if it is not found. Paste it into the system directory of the computer that is producing the 'msdatgrd.ocx' errors.

3. Click on 'Start' and then select 'Run.' Enter the command 'regsvr32 c:\Windows\system32\msdatgrd.ocx' or 'regsvr32 c:\Winnt\system32\msdatgrd.ocx,' depending on the name and path of your system folder. Press 'Enter.'
4. Reboot your computer to complete the registration of the 'msdatgrd.ocx' file.

Is your Defrag missing, or just broken?
1. Open 'My Computer,' right-click on a hard drive and go to 'Properties.' Navigate to the 'Tools' tab.
2. Your Defrag is missing and needs reinstalling if: 1) the 'Defragment Now...' button is missing or grayed-out, or 2) when you click on it you get an error message reading, 'The Disk Defragmenter is not installed on your computer'. To install it, double-click the 'Add or Remove Programs' icon in Control Panel, click the 'Install/Uninstall' tab, and then follow the instructions on your screen. Skip to 'Reinstalling Defrag.'

3. Your Defrag is broken and needs repairing if: 1)you are able to open the Defrag program, but nothing happens when you click 'Analyze' or 'Defragment,' or 2)You receive the error message, 'Windows cannot connect to the Disk Defragmenter engine.' Skip to 'Repairing Defrag.'
Reinstalling Defrag
4. In your main hard drive, find the c:\Windows\Inf directory. If your system directory is not on your c: drive or not named Windows, find it by clicking on 'Start,' then 'Run' and typing %Windir%\Inf in the box.
5. Find the file named dfrg.inf.
6. Right click the file and select 'Install.'
Repairing Defrag
7. Click 'Start,' then 'Run,' and run this command: regsvr32 dfrgsnap.dll
8. Click 'Start,' then 'Run,' and run this command: regsvr32 dfrgui.dll
9. Run Defrag.

1. Click the 'Start' button, then enter 'Dcomcnfg' into the search box and press 'Enter.' Wait while Windows configures and launches the Microsoft Management Console (MMC) Component Services Snap-in application.
2. Double-click the 'Component Services' link in the left side of the MMC window. Double-click the links underneath to navigate to 'Computers' > 'My Computer' > 'DCOM Config' > 'Microsoft Windows Remote Shell Host.'

3. Right-click on 'Microsoft Windows Remote Shell Host,' then click 'Properties' when the pop-up menu appears. Wait for the 'Properties' window to display, then click the 'Security' tab in the 'Launch and Activation Permissions' area.
4. Click 'Customize' and then the 'Edit' button. In the 'Edit' window, assign the following permissions:'Everyone -- Local Launch and Local Activation''Network Service, System, Administrators Group, Interactive--Local Launch, Remote Launch, Local Activation and Remote Activation' (enable all of the checkboxes)
5. Close the MMC snap-in utility. Reboot the computer for the changes to take effect.

1. Restart your computer in safe mode. If the computer is non-responsive, hold the power button down for 10 seconds or until the computer shuts off. Press the power button again and as the computer starts up, hold down the F8 key until the Boot Menu appears. Using the arrow keys, click 'Safe Mode' and press 'Enter.' Booting in safe mode will take much longer than a regular boot up. Log in as administrator by entering the administrator password in the 'Password' field. If there was no administrator password set, leave it blank. You can also log in as any user with administrative access.
2. Use your anti-virus software to scan your computer for viruses or spyware. Choose to scan all files on all hard drives. This may take a long time depending on the size of your hard drive and speed of your computer. After the virus scan is complete, delete all detected viruses. Refer to the anti-virus user documentation for more information on running a complete scan.

3. Run System Restore by clicking 'start,' then 'Help and Support.' Under the 'pick a task' tab, click 'undo changes to your computer with System Restore.' Click 'restore my computer to an earlier time' and then click 'next'. On the calendar, click a bold date from the calendar prior to the date you noticed the error. Click 'next' and follow the onscreen instructions.
4. Install the latest service pack for Internet Explorer 6. Microsoft Support article 328548 notes that IE group policies may cause an access violation in Winlogon leading to the C00021A error. Alternately, installing the latest service pack for Windows XP will install Windows critical updates as well as IE updates.
5. Restore the default Windows Graphical Identification and Authentication (GINA) file. Microsoft Support reports that many STOP 0xC000021A errors occur because the GINA file has been replaced by a third-party program (see reference 1). To verify your GINA version, click 'START', then 'Run'. Type 'regedit.exe' (omit the quotes) and click 'OK'. Scroll down to the following registry key 'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon' and on the right hand pane look for the value 'GinaDLL'. Double-click this value and in the window that opens ensure that 'value data' is set to MSGINA.DLL.

1. First try to run the disk repair utility by using an alternate boot-up process. Turn your computer on and tap 'F8' while it's booting (or whichever key is listed on your screen during start up). This will take you to a boot menu with boot options presented. Choose 'Safe Mode' and continue booting. This mode is a stripped-down version of Windows without most drivers loaded.
2. Go to 'My Computer' from the 'Start' menu and highlight the drive on which you're experiencing the NTFS errors. Right-click on the affected drive and choose the 'Properties' option. This will open the drive properties window. Select the 'Tools' tab and select the option to 'check the drive for errors.' The system will then run through the drive check utility, repairing the NTFS error present.

3. If that isn't successful, access the repair console by placing your Windows System Installation disk into the drive. Turn your computer off, and then turn it on again to load the disk. Choose 'boot from disk in CD-ROM drive' during your computer's boot-up sequence (tap F8 as you did before to enter setup and change the boot option). Choose to enter the repair console when offered the choice on screen. The repair console will appear as a text prompt, for example 'A:\>.' Enter 'chkdsk a:' with the actual drive letter of your troubled drive replacing the 'a:'--chkdsk will run on your system and repair the NTFS error on the affected drive.
4. Move the drive to a second PC if the affected disk is your boot hard drive and you cannot access safe mode and your system installation disc is unavailable. Connect the hard drive to the second PC and use the safe mode on the unaffected PC's operating system to repair the drive.

1. Press 'Esc' if you get an error message such as 'Cannot Empty the Clipboard.' This is a temporary fix, but may prevent you from losing the information you want to copy and paste.
2. Go to the 'Start' menu. Click 'Run' and type 'clipbrd.exe.' Leave the window with the Clipboard open for a while. This may resolve the problem.

3. Open Task Manager. Click the 'Process' tab. Turn off the process called 'rdclip.exe.'
4. Open Microsoft Excel. Click 'Tools' and 'Options.' Click the 'Calculations' tab.
5. Under 'calculation,' check the box next to the word 'Automatic.' Restart the computer.
6. Try to clear the Clipboard. Open Clipboard and choose 'Edit.' Click 'Clear All.' Also select the 'Collect without showing Office clipboard' choice on the bottom of the window. Click 'OK,' close the window and restart the computer.

1. Back up your entire registry by either exporting it to another file name or saving it to an external device, such as a USB flash drive, external hard drive or a CD. Hopefully you won't need this, but it's better to be safe.
2. Set a system restore point in either Windows XP or Vista. This allows you to go back to a stable system that existed before you edited the registry.

3. Click on 'Start' and type 'Regedit' in the run field, or in Vista, click on 'Run' and then enter 'Regedit.' This brings up your registry editor.
4. Know specifically what you need to change. The Windows registry is huge and navigating it line-by-line is almost impossible. You can also search the registry for specific keywords related to your problem.
5. Select the area you need to edit from the left pane of the editor. Lines of code will appear in the right pane, where you are able to make your changes. Be careful not to make a mistake.
6. Save your changes. Close the editor and reboot. Any changes you made will become effective during the boot-up process.

1. Make sure that you have run your virus scan on your computer and cleared out any possible viruses or threats that your computer may have.
2. Next you will need to go to either CNET.com or malwarebytes.com and download the free malwarebytes malware removal software.

3. When the prompt pops up to run or save, click on save and select the directory you want to save it to. I always save these because you never know how long the company will supply these services for free so it is useful to save it in case you ever need to reinstall it.
4. Close all of the programs that are running on your computer such as the internet explorer except for the malwarebytes program.
5. Next you can follow the prompts on screen and install the program.
6. Once the program is installed you should run it on the full scan mode to get rid of any malware your computer may have. This should fix your problem with the internet explorer.
7. Once the scan finishes remove or delete the threats and then restart the computer.

1. Click 'Finder' on the dock to launch a new Finder window. Click 'Macintosh HD' and double-click the 'Applications' folder.
2. Double-click the 'Utilities' folder and double-click 'Terminal' to launch the Terminal.

3. Type the following command in the Terminal and press 'Enter' to disable the problem reporter feature:sudo chmod 000 /System/Library/CoreServices/Problem\ Reporter.app
4. Close the Terminal.