Windows 2000 Reboot Loop after restart.

[Hodoshow]

I'm having a bit of trouble with windows 2000 and a reboot cycle, but the problem has a bit of history.
Orginally the system was running win98 and it was discovered to have a number of viruses. The owner of the computer tried to remove the viruses but then complained about the windows reboot loop. This is when i first received the computer.
I immediately upgraded the ram from 64mb to 256 and the system ran without fault. I checked the system for visuses using the latest Avast! without concern.
Feeling quite chuffed with myself over such an easy fix i moved to install win2k but the reboot loop appeared during the final stages of installation as well as a blue screen error message and missing dll files during installation. Thinking it was a hard drive problem i tested a new hard drive but still encountered the reboot loop during the final stages of installation. I removed the new hard drive and completed the installation in another system. Returning the hard drive to the faulty system i have found that i could run win2k successfully for any length of time but if i was to restart the system the reboot loop kicked in. If i leave the system off for a number of hours it will start up successfully but it goes back into the reboot loop if restarted. I'm a little baffled by this behaviour.
I have tried swapping motherboards but i encountered the same trouble with my spare (although i'm not convinced of the spare MB's integrity).

Does this problem and behaviour sound at all familiar to anyone? Is it virus related or a problem with the motherboard?

Any help would be appreciated.

Current system (with upgrades)
CPU Type Intel Celeron, 900 MHz
Motherboard Shuttle MV19
Memory 256MB SDRAM PC133
BIOS Type Award Modular (04/13/01)
HD 80GB IDE100

[snowmonkey]

I have seen the reboot loop issue with Windows 2000 before (first hand, on my brother's PC).... in his case, the master boot record was messed-up, so all I did boot the system with Win98 Boot disk and on the prompt type fdisk /mbr..... that all it took for him, give it a try.


Cheers

[Hodoshow]

Thanks for the suggestion SnowMonkey, sounded like a logical solution to the problem but to no avail.
Still encountering the reboot loop

Any other ideas??? Anyone!!!