I know that feeling...like WTF?!?!
What motherboard?
What video card?
Does your computer give you any beeps that might indicate a specific problem?
Can you hear the cooling fans/chipset fan/drives spinning up?
Have you tried the PSU in the other computer along with the video card?
I'm assuming you used the same monitor with that other computer?
How do you know that the mobo/PSU were the only items destroyed?