I would suspect the psu. If you have a multimeter, you can test it.
Take the psu out, and have 1 ide drive attached. It can be an optical drive or an old hdd, it doesn't matter. Plug the psu in, and connect the green wire to the black wire, in the main mobo harness. You can then use the meter to test the voltages at the molex connectors. If you dont get close to 12 and 5 volts, your psu is dead.