spontaneous shutdown and video errors

[Bluff]

Hello all,

was using my computer as normal
(Athlon XP 64-bit 3200
GA-K8NS mobo
1 gb ram
Ati X800 Pro
SATA HDD
Win XP Home)
and plugged in a usb device (my smartphone) and at the same time my usb mouse turned off. Attempts to turn it back on told me that 'a usb device has malfunctioned'. Anyway, I restarted, without the mouse, and plugged in the mouse. It wouldnt work. I took it out.

A few seconds after that, it turned off. So I started it up again. It began to load windows, then turned off. I turn it on, it starts the POST, it turns off.

I manage to get it into Safe Mode, and everything (except the mouse) works fine. So I restart. It starts to load windows etc...
Then after a few more tries, after showing the windows loading logo, I get a bluescreen telling me the ATi driver is in a loop. So I turn it off, then start in safe mode. But when it gets to safe mode, it crashes!

Sorry for the long explanation, but since I can't see whats causing this, thought I'd better explain it fully. This is so random!

edit: after writing this, it wont turn on at all!

Any thoughts?!