I recently thought that the motherboard in my machine had died. No power on light on the front panel, motherboard power light WAS on, nothing showing on monitor except a flashing ready light, hard drive not powering up or spinning, no activity of any kind. Replaced motherboard with an exact make and model #.When attempting to boot the machine now, the power light on the PSU doesn't light.Whan the power switch is pressed, the PSU comes on for 1-2 seconds then goes off.Does the same thing when pins 14 and 15 are jumped over. Tried a known good PSU from another machine. It passed the pin jumper test. Once connected to the machine, it does the same on/off thing like the original. Suggestions anyone? All welcome. Also tried resetting the CMOS,just in case.