Is my system dead?

[badger]

Intel E6850
Asus P5K-E
4GB OCZ RAM
HD3870
1TB Samsung
Corsair 620W PSU

My 8800GTX died a week or so ago, just came up with a load of corrupted graphics. I replaced it with a 3870 I had, and everything has been working fine until just a second ago. I was just typing on a forum when my screen went black and one of the fans in my system started spinning at full speed, I think it was either the CPU or GPU fan. Reboot did nothing, fans go full and the display stays off.

I replaced the graphics card with another two different cards, same results but less noise, so I assumed it was the graphics card fan that was going full tilt.

What's most likely here? I don't think it's the graphics, only bought the 3870 less than a year ago and it's only been used for a very short time, and replacing the card didn't change anything. Is my motherboard dead? CPU? RAM?

[GoNz0]

got a spare PSU ?

[badger]

Yeah, I've got a spare PSU, but is that likely to be the problem?

[strike-down]

It can be sometimes. But you dont know till you try

EDIT: Have you tried resetting the cmos?

[badger]

I've replaced the motherboard, get exactly the same behaviour. Before I did that I tried another CPU, and it still did the same. So I don't think it's the motherboard or CPU.

One thing I've noticed, before it died the system would start up for a second, power down, then start again. Now it just powers up straight away. Would that indicate a particular problem somewhere?

[badger]

Ok. I replaced the PSU and there was no change. Then I left the new PSU in there but changed the graphics card, and it worked. So it looks like I have a dead graphics card at least, but when I tried that before with the other motherboard and PSU it didn't work.

So what's most likely here? Is it a dodgy PSU that blew the graphics card, or a dodgy motherboard? I'm reluctant to test this out in case anything else gets wrecked.