RE: BSOD on startup
With all you've done, including reformating and reinstalling the OS, I'm agreeing with the hardware theory.
Now the problem is tracking down which piece. Virtually all system hardware will have an IRQ, so I don't know if that clue helps or not. Go to device manager and see if any hardware conflicts present themselves there(I'm sure that's been done already). If not, list all devices by connection and list by Interrupt Request(IRQ). Make a list. Disable, remove or exchange each non-essential device systematically. If it appears to be something on the MB, don't despair, it could just be the power supply.
WARNING!!! In doing this once, somehow I disabled the HDD controller and all hell broke loose! Talk about making a bad scene worse! :B