what i'm thinking[and partially what i think warez monster was getting at] is that it sounds like the power supply. sounds to me like the PS can't handle the amount of stuff plugged into it, wattage-wise. i've seen this exact thing happen before after adding something to a PC with a low-wattage power supply. at any rate, yeah i'd debug it just like he said.
MY 1337 SYST3M:
(1)case - generic
45jiga-hurts intel pentium VIIteen hollywood
some more ram.
asusapaloozatron v7542 mobo