My computer was running fine. It now won't power up after properly shut down the night before. Pushing the power button will not power anything up (no PSU fan, no CPU fan, no beep, no light). I tried to remove everything except CPU, memory, video. I installed known good PSU, memory and video card. The only way for me to power it up is jumping green and black wires at 20-pin connector. It then continues to boot up OK. While in the BIOS set up screen i can power it down by pushing the power button. I don't really understand how the power button work. I can power down but won't power up with the button. Please help. Thanks None

Try another power supply.

The power switch brings the power supply up out of standby to full power. The motherboard then checks the voltages and if they are all within tolerance, the motherboard sends a 'power good' signal (the green wire that you jumpered) to the power supply. If the power supply does not get this 'power good' signal it shuts back down. Since you tried swapping power supplies, it might be that the motherboard is failing to correctly sense that the voltages are ok.

Take a look at the connection from the on/off button to the motherboard. The one on the front of the computer...not the one on the power supply if it has one. Unplug and reset. Still nothing? Unplug it and using a screw driver short out the two pins that connect to the front panel...Just a light touch. You do not have to keep it connected. If it starts the problems in the front panel on/off switch. So if the power supply is good and the front panel switch is good then the problem lies in the middle.