Desktop will not start.

Hello,
Please help with startup problem.
After line power fluctuations and automatic shutdown, my Gateway 560GE will not restart. I tested the power supply and, with jumper applied, the cooling fan runs and supply output is 11.87V but the computer will not start.
When power cord is connected and the On switch is pressed, a small green LED on the motherboard flickers intermittently along with simultaneous brief revolutions of the cooling fans. That is the only response and it ends after about 8-10 seconds.
The indicator light on the power switch never illuminates and there is no response from the drives. I have held the power switch in with all connectors removed to discharge any capacitive charges but still no startup.
Thank you.