I have a computer that will boot up part of the way then go back and restart booting up. The hard drive had a virus on it so I externed it to another computer and removed the virus.This hard drive with operating system will not start on any other computer as I get the same symptoms. It starts and asks which mode I wish to start in. Any mode I choose will not allow xp to start up and the computer reboots again. All modes include "safe mode" to "last config that worked".