Try a Repair Install
with your WinXP Bootable CD.
If Repair option fails you will have to do a Clean Reinstall of WinXP as a last resort.
1. Boot with your WinXP CD
2.At the "Welcome To Setup" screen, Choose
the option: To setup Windows XP now, press ENTER.
DO NOT choose !!!!
To repair a Windows XP installation using Recovery Console, press R.
IGNORETo quit Setup without installing Windows XP, press F3
3. Accept the License Agreement and Windows will search for existing Windows installations.
4.Select the XP installation you want to repair from the list and press R to start the repair.
If Repair is not one of the options, under the Circumstances you are in the next option will be Clean install
5. I this does not work it might be your memory --download and burn to cd memtest (http://www.memtest86.com/
) and test your memory for errors.