Help: Computer Continually Rebooting

[GMAN51]

I recently swiched out the hard drive on my Shuttle PC. I then installed Windows XP SP2 and updated most of my drivers. Windows update wanted to do some updating so I allowed it to download files. While it was doing this I got caught up in other things that I was doing and forgot about the pc. After a rather long time of ignoring the Shuttle I suddenly heard it reboot. I looked over and as windows was beginning to load the PC rebooted again. This rebooting continues indefinitely. I very much appretiate any help with this problem. Thanks

Here are my specs if you need more just ask.

Shuttle PC
P3 2.4ghz
1G Corsair DDR PC2700
ATI 9700 Pro
Western Digital EIDE 160GB HD (It replaced a WD EIDE 80GB HD)

Again, thank you for the help.

[Alfie]

Have you tried to boot the computer in safemode?