Mouse, & monitor stopped working and pc restarts itself

Hello all,
I hope one of you can help.
I am running WINXP on an 1800 AMD Athalon.
The problem started yesterday when i switched the computer on, and the mouse wasn't working, so i swapped the old mouse with a brand new mouse, but still no joy. So a bit later on in the day after having no joy fidding with the mouse settings etc ( in device manager it doesn't even detect a mouse being their) i dialled up to the internet using keyboard shortcuts and the pc restarted it self, and did it a number of times.
So i switched pc off for a bit, and then when i came to switch it on the monitor doesn't come on. I know the monitor is not at fault as i am using it now on my old computer. The fans inside the computer are all powering up, although there is no beep. I did wonder if this maybe all the cause of a virus ? however i am running Norton which is always updated.
but i don't know what to do now, as i am a bit stuck now that the monitor has stopped working. So all help would be much appreciated.

It could be a hardware malfunction.

It could also be benign oversight. For example, this story I convey happened to me about two weeks ago:

I have a breakout ASIO audio box and a PCI card. Suddenly some of my audio applications were freezing up, others failed to recognize the device altogether. After updating the drivers, pulling my hair out, checking all the connections I finally got around to flipping the panel off the case.

Know what I found?

The PCI card had been unseated from the socket. I had recently removed a piece of audio gear from my rack, and apparently in doing so I had given a good enough tug on the cable connected to the PCI card that the card unseated but still seemed tight in the case.

After pushing down firmly, all related problems ceased to exist! 10 seconds to fix it. Hours to find the problem.