Dear sirs,
I need your help.
Equipment: PC desktop Dell Inspiron 545 with Windows 7 Home Premium 64-bit.
Problem: I connect the PC to the AC voltage, then I press the power switch button located at the front of the case and the PC does not turn on immediately, I need to keep the PC connected to the AC for several minutes (more than 30 minutes) and then press the power switch again several times until the PC finally turns on. This is happening every time that I want to turn on the PC. Once the PC turns on it works very well.

I have checked that the signal +5VSB is on all the time the PC is connected to the AC. But, I have notice that when I press the power on button, the signal PS_ON# (active low signal , generated by the mainboard) is not going from +5Vdc to a value of +0.8V or less, it is like it try to go low, the digital tester shows that it goes to +3.50V, so it keeps in a high state. The power on switch/button is okay, contact open and close okay.

To test the power supply (PSU), I have disconnected the PSU from the mainboard, connected only one DVD drive to the PSU, and as soon as I short the PS_ON pin to ground the power supply turns on with all the voltages okay. So it seems that the power supply is okay.
Then, I cut the PS_ON green cable to keep this signal disconnected from the mainboard, and I short the PS_ON to the PSU Ground at the PSU side with the purpose to turn on the PSU as soon as it is connected to the AC. The PSU turns on when it is connected only to the DVD Drive, but the PSU does not turn on when the power supply is connected to the mainboard, also I have noticed that the Power Good signal (generated by the power supply) is kept in 0 voltage and the only voltage is at the signal +5VSB.
When, after waiting several minutes and the PC finally turns on, I test that all the signals and voltages are okay, the PS_ON is 0V, the Power Good is +5V.

This problem of having to wait several minutes to turn on the PC is like the PSU or the mainboard would have a bad capacitor or circuit that need more time to be charged with the proper or operational value. It is like something in the mainboard is preventing the PSU to turn on immediately.

I don't know why the power supply does not turn on and put its the Power Good signal in +5V high state when the PSU PS_ON signal is connected to the PSU Ground and the P1 PSU connector is connected to the mainboard? The PSU only turns on immediately when it is not connected to the mainboard. Maybe the mainboard is short-circuited? But why after several minutes the PC turns on and works perfectly?

As a next step, keeping the PS_ON short-circuited to ground at PSU side, I was thinking to cut the Power Good grey cable to keep this signal disconnected from the PSU, and short the Power Good signal at the mainboard side to one of the PSU +5V voltages lines, so the mainboard will see always a good +5V Power Good signal and the CPU could start its rutine. But if the PSU does not turn on this try will not work too.

I will appreciated very much your help to solve this problem.

Kind regards,