First of all, I have a Gateway Model FX7026 desktop computer. My daughter was using it when suddenly the monitor screen becomes black. She tried to turn the computer on again but nothings happen. I open the computer and tried to plug the power cord and turn it on but nothings happen..The computer does not turn on. The following is what I have done and observed: (1)When I plugged the power cord to my computer, the motherboard standby led green turns on even not switching the computer power switch to on. (2)When I switch on the computer, the CPU fan will just rotate once and then stops also the motherboard standby led remains on. The power switch LED in front of my computer does not turn on. In other word, the computer does not turn on (3) I reset everything but the same problem. (4) Tried to remove one memory (Channel B-DIMM0)module, the video card, and other drives. I Just left one memory card and the motherboard with the CPU (with CPU Fan) and the chipsets (North Bridge and South Bridge). The same problem occurs with standby_led on. I even put a new memory(from my other computer) but the same problem. (5) Verified the PSU to be good by shorting the green and black wire of the 20-pin PSU plug. Still, Tried to use another PSU with higher power rating but still the same problem.. What seems to be the problem? Any help would be much appreciated.