How to Repair and Troubleshoot a Dead ComputerPCComputer does not turn on and appears completely dead.Here are the steps to be made.

Check if the power switch is turned on, Try to plug a lamp into the wall socket to make sure power is available Check if the power cord properly connected to the wall outlet and the computer power socket. Check if the cord look OK and undamaged? If it looks damaged, replace it; Open the system unit and push down on all the chips, Video Card, Sound Card, Modem or LAN cards, Memory and the CPU to make sure they are seated properly.
But before going through with this process, you should turn your Computer off and disconnect the power cord. It is also important to ground yourself by touching the frame of the case before going through the troubleshooting process. All of your PC’s components are sensitive to static electric charges.

Check the power connector from the power supply to the motherboard… Pull out and reinsert all the cards; try placing them in different slots,
Take out all non-essential parts so that only the basic part such as the motherboard, power supply, display card, controller and drive are left. You can pull-out the cards by removing the screw.

Replace each part one at a time, until the problem reoccurs. When you replace a part and the computer stops working, You know that part is the reason for the problem. It can then be replaced If the computer still doesn’t operate, Remove all the remaining cards including the display card and floppy controller. Turn on the power and check if the power supply is running. If it runs, one of the cards you just removed is bad.

Clich here for tutorial with screenshots