dag nabbit, power supply

k, my friend brought his computer to my house so he can bum of my internet, it was runnin fine ever since, but this one night, it decided not to boot up. He was at my house the night before and was using the internet and shut his whole system down. It just wont boot up at all. So im guessing the power supply is wack. So we make sure by checking the cables and if eveything was connected, still nothing, no fans or anything on. I have the same power supply he does, i decided to put mines in his, because i knew his PS was kaput. NOTHING, so i decide to put my power supply back in my computer, now my computer wont boot at all, just like his. So i use my trusty "powered by honda" voltmeter, both power supplies are dead.

My friend and I are planning to get new PS. whats worrying me is that i think my friends mobo is causing the trouble. So if i replace mines, i'll be fine, but if we replace his, the new power supply will be good as garbage. any ideas or suggestions?

Both our computers are fairly new
1.6Ghz P4 300W ps (1 yr)
2GHZ Athlon 300w ps (5 months)