If you recently installed new hardware, go into BIOS setup and update the ESCD in order to notify it of a new hardware setup. Try accessing Safe Mode by repeatedly pressing F8 on startup. If you can access Safe Mode, run spyware and virus scans to hopefully solve the problem. If you can’t even get into Safe Mode, you’re out of luck and are forced to format and reinstall using the Windows CD/DVD. You will loose any existing data on the hard drive.
Computer rebooting on Startup