I have:
Gateway GT5408
Win 7
Intel Core 2 Duo E4300
320 GB SATA II HDD
2048 MB PC2-420 DDR2 533 MHZ ULTRADDR2
PSU ATX-300-12E REV DR
I had to remove my PSU to replace my DVD... Now the computer doesn't come on. The fans turn and immediately stop when power is plugged in, and the green MOB light (CR3J1) remains on. The power button does nothing. When I unplug it, after a few seconds the light goes off with a faint power down beep from the PSU. Everything was working fine before.
Please help!

Thanks!!