Help! Sudden overheating issue!

[megakid]

I've just got back from university and found my PC absolutely sweating it's nuts off - i'm trying to type this quick to shut it down again before im risking more damage but here's how it went:

It's spec is this:

SN85G4V2
Sk754 A64 clawhammer 3400+
1Gb corsair RAM
1 * 74Gb raptor
1 * 250Gb maxtor drive

hmmm, dont think there's much else...
I left the PC running all night last night (not unusual), it's a shuttle machine but I have fitted an extra fan and have Cool'n'Quiet installed and working so it runs coolish (not half as cool as desktop machines).
I came home just a minute ago and found it absolutely boiling it's self - the I touched MSN messanger and got a Blue screen of death - I touched the heatsink attached to the CPU on the rear and nearly burnt my fingers. I instantly went into bios and saw a 94C reading from the CPU and the whole case was like a heater.
I turned it off, took of the case asap and took it outside for a cool off period. I've now plugged it back in, everythings working fine but it seems to be running extremely warm! CPU temp is now 83C and rising (0% CPU usage).

What can I do?! I've got a major major assignment in for uni tomorrow and I NEED my PC. It's been reliable for my 2 years here and NOW, on a night like tonight, it decides to go boobies up.

Is this a software problem? would a windows reinstall possibly work?
How can i narrow it down to hardware/software? I'm just about to sit in the bios and see what the temps do in there - that should be absolute 0% CPU right?

Thanks!!!

 

[megakid]

Im currently at uni but when I get chance I'm going to strip it down, give it a good clean out and re-seat everything.

Hopefully that should cure it and no damage has been done!

Fingers crossed!

 

[megakid]

The thing I dont understand is the machine had been running all night (whilst I was in bed) and then I got up and went to university when it was absolutely fine - came back 10 hrs later and it's killing itself.
There's no way the heatsink moved as my room was locked and nothing could have happened to it.

anyway, right- Ive just completely stripped the shuttle down cleaned everything I could and reapplied Arctic silver 5 to the CPU (followed instructions as always) but the high temperatures are persisting.

Ive just ensured cool n quiet is on but it's still at 65C at idle with fan on full (4300rpm) so thats with the cpu being auto underclocked to 36% of 2.4Ghz and down volted from 1.5 to 1.3. I can physically feel the heatsink much hotter than usual. I dread to think what would happen if I try and play a game on here with my 6800GT kicking out heat as well.

The machine is running as normal otherwise.

Is there any other possible causes?

Could the CPU be overvolted if a mosef on the motherboard failed?