XP rebooting at login
 

Hi I have a WIndows XP Pro computer which gets in a restart loop. Cannot access Safe Mode or Normal Mode. Tried running XP Repair - no difference. Tried Hard disk in an identical computer (same Motherboard, CPU memory etc...) Still rebooted. Ran a fresh install of XP on another disk and it booted fine. Imaged disk - same thing happened. Ran Virus scan on disk - Clean. Must be a device driver or corrupt boot file issue. Any suggestions on diagnostic software (note cannot boot to Safe Mode) to determine whats faulty ????