Since your power supply appears to be OK, it's either the motherboard, memory, or video card (for some silly reason newer PCs won't boot if there's something wrong with the video card).
Since you have access to another PC, I recommend testing your video card in the other PC first. If that works, test your memory by removing all of it and tying to boot with only a single stick inserted at a time (or you can take all of it out and test it out on the other PC).
I had something similar happen to me a couple of weeks ago (it turned out to be the motherboard).
Good luck
Dave