I tried replacing my mb and cpu, but I still cannot get into windows. The boot process goes fine until right before the Windows loading screen where the screen is black and a bar runs across to the right. A blue error screen comes up for about 0.0001 seconds and then the computer reboots. Safe mode brings the same result, stopping at the driver mup.sys (which I have) and blue screen - reboot again. The funny thing is that the hard drive(s) work on my other computer just fine. *The first time I got all the parts, it worked for about a day. But when I turned it on again, the error started occurring incessantly. I tried the replacement of mb and cpu, but still the same thing. Could it be the DDR stick? BIOS setting(s)? Would you please help me?

Did you reisntall Windows on the hard drive after replacing the motherboard and CPU? Different motherboards may require different drivers to be installed with Windows.

Since I havre Windows XP, can't I just reinstall over (update) the current hard drive, allowing for me to maintain what is on it?

WinXP is not very freindly towards hardware change however it should be ok to do an install over the top and retain the information. Make sure that none of your hardware is overclocked as this will cause Blue screens during install and double check the partition and HDD integrity information with one of the OEM HDD utlities available for download

By the way, my motherboard is ASUS A7N8X Deluxe. I am scared to do the reinstall because when I first had a clean hard drive for the initial mb and cpu, I would get a windows xp setup error right after it automatically reboots after loading system files during setup.