desktop crashing/BSOD/overheating

On sunday night while having a nap I came back to PC to find it blank. Everything still on, but no response. So power cycled, then BSOD after it loads the first red dot in Windows 7. 0x0000007E

I decide to leave it over night, and next morning it boots. Dies after about 30 minutes, was only running firefox and running a backup. Same error, though when I tried to reboot a couple times it gave errors ranging from page fault to satasys to upnp.sys to 0x0000007A. I have tried booting into the w7 DVD but it crashes as well. Strangely I booted to ubuntulive cd with the GPU in, got to the desktop fine no problem.

I decide to take out the 5870 GPU and use onboard but no luck. Tuesday I buy a new mobo (same model, newer version), and it works fine from the onboard, but same issue with GPU. I run minecraft for about an hour, seems solid.

Come yesterday I buy a new graphics card, 6970 and it seems to work fine. Again minecraft seems fine.

Come today, 5 minutes into crysis2 it dies to complete freeze with sound looping. Reboot to BSOD.

Leave off for 5 minutes with 30" desk fan blowing into case, boots fine. I've got work to do but later I plan to do a CPU-only stress test first with fan on, then fan off.

I guess it is possible it is the PSU, or the CPU, especially as it seems the old mobo and gpu died so maybe the PSU is having power issues or output problems.

This problem actually seems like a power supply issue... I assume you cleaned out all the dust and that you have proper cooling for your CPU. So temperature shouldn't be the problem here.

How many watts is your psu rated for?