Hi everyone, One of mine friends ask me to fix her nephew computer Compaq P4 desktop with the model: "Compaq Evo D51C". This computer has no power when I press it power button. Before it works fine, but one day it stops working. I thought the power supply has problem, so I replaced it with my working power supply, but it still does not work. Now I thought there is something wrong with the power button, but it is difficult to check that. I aslo think that the motherboard has problem. Any suggestion on how to troubleshoot this computer? Thank you very. Note: this computer runs Windows XP and I heard that her nephew plays games around 10hrs per day on this computer

It is rare for a power button switch to give you problems. Check the old PS. See response 4 in this: http://www.computing.net/hardware/w... If it's fan no longer turns easily, and/or if the PS stinks of something burnt, it probably failed, and a PS sometimes fries the mboard or something else connected to the mboard when it fails. The cheaper the PS, the more likely it is to damage something other than itself. E.g. if it is a Bestec PS, it probably fried the mboard. If in doubt, if the wiring of the 20 or 24 position main connector from the PS is the same - same colors of wires in the same positions - try the orginal PS in your computer. If it's already dead it can't hurt your computer.

Yes I agree power switch failure is rare,check all fuses,you should have one "onboard" and one in your plug,second checkall connections

Thank you very much folk for your suggestions.

"check all fuses,you should have one "onboard" and one in your plug" That is often not the case. Mboards often do not have fuses, and even if they do I have never seen them identified in any mboard manual, and there may be no markings on the mboard that identify them. Computers sold in North America have no fuse in the power cord. The fuse inside the PS usually does not blow when the PS fails, and if it does, replacing it almost always results in it blowing again immediately after the computer is booted, or even immediately after the PS is plugged into live AC.

This may help, or if not go to the same site and search by your serial number since there are variations on the Evo 510. http://h20000.www2.hp.com/bizsuppor... If you can locate where the power switch leads go to the motherboard, you could pull the plug and touch the pins (carefully) with a paper clip or screwdriver blade to bypass the switch. The switch is probably fine, and the power supply and motherboard are probably dead. These SFF computers are not likely to be worth fixing unless you have organ donor machines handy, and they have the same weaknesses. Power supply test info: http://www.duxcw.com/dcforum/DCForu...

Don't completely ignore the power switch, I once had the plastic piece on an old Compaq of mine break or it came out of it's housing or something. Don't remember the specific problem, but I do remember that it was just the switch.