|You might have a memory issue. Download Memtest, when you open it it will allow you to make a bootable floppy or CD so you can test your RAM from outside of windows. (make sure that the drive you are using is first in boot order first). |
If any of the tests fail or fail to complete, see if you have more than one memory stick, if you do, test each one separately, replace as needed.
If you cannot boot to the Memtest or you cannot access your BIOS settings, you may have a problem with your motherboard.
If these check out ok, try booting to your Windows disk, if you are able to, do a repair from the disk