Diagnosing a Hardware Problem
1. Shut your computer down and open the case according to the manufacturer's recommendations. Examine the data (flat) cable going into the back of the drive. This cable should have 80 internal wires, which can be counted by running a finger across the cable. If the cable has 40 wires, it needs to be replaced with an 80-wire cable, which can be purchased from any computer store.If you have a Serial ATA hard drive, skip this step.
2. Close your computer's case. Turn on your computer. On the initial screen displayed when the computer is turned on, you should see instructions to hit a key (usually the 'Delete' or one of the 'F' keys) to enter motherboard setup. Tap this key until the setup menu appears.

3. Look for an option in the motherboard setup utility labeled 'Fail Safe' or 'Safe Default.' This will disable any special options that your motherboard may be using to maximize the speed of your hard drive. Save and exit the setup utility and allow your computer to restart. If Windows boots successfully, there is an issue with your hard drive. Contact the hard drive's manufacturer for further assistance. If you continue to have a problem, use the setup utility to revert your motherboard to the previous configuration and continue to the next step.
Repairing a Damaged Boot Sector (Windows XP)
4. Turn your computer on with the Windows XP disc inserted into the drive. As the disc is starting up, you will see a message telling you to hit the 'R' key to load the Windows Recovery Console. Hit 'R.' You may need to enter the administrator password for your computer. After this, the command prompt will load. You will see a monochrome screen with a blinking cursor.
5. Type 'chkdsk /r' without the quotation marks and hit the 'Enter' key. This process will scan your hard drive for physical errors and attempt to repair them. It may take some time to complete.
6. Type 'fixboot' and hit 'Enter' after the scanning process is complete. Hit 'Y' to confirm the process. This will replace the hard drive's damaged boot sector. Restart your computer, and Windows should load.
Repairing a Damaged Boot Sector (Windows Vista or 7)
7. Restart your computer with the Windows Vista or 7 disc inserted. You may need to enter basic information such as the local language and time before you are presented with a menu. Click 'Repair your computer.'
8. Select the Windows installation to be repaired if you have multiple versions of Windows installed on the same computer. Click 'Next.' In the next screen, click 'Command Prompt.' This will bring you to a monochrome screen with a blinking cursor.
9. Type 'bootrec.exe /fixboot' without the quotation marks. This process will replace the hard drive's damaged boot sector. Restart your computer, and Windows should load.