XP does not start and computer keeps rebooting

My computer keeps rebooting as soon a user loggs in, no matter which one. If
left alone the C reboots after a few minutes. There is no posibility
whatsoever to access.
I transferred the harddisc to another computer for a thorough virus scan,
but the problem remains though some virus where removed.
I suppose I got some sort of malvare. The problem i how to get rid of it.
Can anyone help?
.

Relevant Pages