1. Start your Windows Vista computer in 'Safe Mode.' Hold the F8 key as the computer starts. If you can start the computer in safe mode, you probably have a software-related issue (or possibly a hardware issue). If you can't get the computer to go to safe mode, you most likely have a hardware-related issue.
2. Uninstall recently added programs to your computer if you started having problems with the computer soon after adding new programs.

3. Use the 'System Restore' function to return your Vista computer to a point in time when the computer functioned without problems. Access 'System Restore' by clicking the following options in order: 'Start,' 'All Programs,' 'Accessories,' 'System Tools' and 'System Restore.' You may have to use the administrator login and password to restore the system.
4. Restart the computer to complete the 'System Restore.' Try using a couple of older restore points if the first restore point doesn't work.
5. Check your hard drive for errors while in safe mode. Go to the 'Start' button and click 'Computer.' Hover the cursor over the drive you want to check and right-click it. Select the 'Properties' option. Use the 'Tools' tab and click 'Check Now' under 'Error-checking.'
6. Complete the process: Place a check mark in the boxes to 'Automatically Fix File System Errors' and 'Scan for and Attempt Recovery of Bad Sectors' for a thorough attempt at repairing the hard drive. Use the 'Start' button to begin the hard disk repair. You may be prompted to restart the computer to begin the hard disk repair process.
7. Listen carefully to your computer. Feel it to see if the hard drive starts spinning when you power up the computer. If the hard drive is spinning, but nothing appears on the monitor, shut down the computer. Open the housing and reseat the memory modules by taking each one out and firmly putting it back in place. Start the computer again. You can take out memory modules and reposition them to check each module through trial and error. If the computer starts operating when certain memory modules are removed, these modules are bad and need to be replaced.
8. Remove recently added hardware that may cause a conflict with the computer's system. For example, if you added a video card right before the problem started, put the old video card back in the computer and restart. Get updated drivers for the video card or other device if you want to use the troublesome device in the future.
9. Stop a loop. With a loop, the computer starts normally but tries to restart again and again whenever it reaches a certain point. In safe mode, place a check in the box next to 'Disable Automatic Restart on System Failure.'
10. Reinstall Windows Vista if you are sure the hardware is functioning properly and the problem is software-related. Insert the installation disk in the appropriate drive and restart the computer. Remember: when you reinstall Vista, you will lose everything on the hard drive.