Can you get into safe mode by hitting the F8 key while the computer is booting up? If so then it is usually a drivers problem causing the auto reboot. Disable auto reboot in safe mode to see what blue screen error comes up.
If the computer has SP 2 installed you should see this window when you boot to safe mode.http://www.microsoft...k-safe-mode.gif
use the arrow keys to go to "Disable Automatic Restart on System Failure". Then reboot the computer to see what the error message is. A check at the aumha website will help to tell you where your problem is.http://www.aumha.org/a/stop.php
Do you have your Windows XP CD?
If so, boot up with that and choose "R" at the first menu, that will get you into the recovery console, from there, at the prompt, type in "chkdsk /r" without the quotation marks.
Let check disk run, it may take some time, but when it's finished, type in "exit" and let the system reboot. Hopefully it will fix any system files that may have gotten corrupted.
Go to http://www.knopper.n...x/index-en.html
and get a Knoppix CD. It's free . If you have dial-up like me, it will take a very long time to download, but it really is worth it.
Knoppix is a bootable GNU/Linux operating system CD that runs entirely from the CD drive, without writing anything to your hard disk. It has excellent hardware detection so just about everything is set up automagically.
If you can boot from the CD and use it without a problem, then it is likely that the problem lies with your windows drivers.
If it still reboots automatically, then you might have a hardware or bios setting problem...if it does, you should be able to see at exactly what point it does reboot, so you can get a good idea of what is causing the problem.
This information will prove very valuable in hunting down this problem.