Couple of possibilities
Couple of possibilities, but the most likely scenario seems to be that the motherboard died. Still, may as well try a couple of the simple free options first. Pull the power cable out from the computer and leave it out for a good 15-30 seconds to make sure the PSU capacitors drain. You can press the power button as well to help facilitate this. Then plug the computer back in, give it 5 seconds or so to energize the capacitors, then see if it will boot.
If it still doesn't want to boot, odds are you're looking at a bad motherboard. The PSU is a possibility, but generally if you have a bad PSU, you don't get any kind of movement when you press the power button. I'd be willing to go so far as to say the symptoms seem to fit the bad caps (google it) issue pretty well. For most people that's a death sentence for the motherboard.
What I'd suggest you do is get your brother out to take a look. He built the unit so should be reasonably familiar with its component parts. If nothing else, odds are he'll have an external enclosure you can use to pull the HDD and get the files you need off the drive so you can finish your work on a campus computer or something.