Jump-Starting Your PC

If you suspect that the power supply has failed on your desktop PC, you can try to jumpstart it if you have another computer available. To do this, remove the two power connectors from the motherboard in both PCs. Place the computers side by side, and plug the power connectors from the working power supply into the motherboard in the nonworking PC. (If the cables aren’t long enough. simply unscrew the working power supply, supporting it carefully, and hold it closer to the other PC.)

Next, try to start the nonworking PC. If lights and fans activate on the motherboard, it is drawing power perfectly well, and you can be certain that the power supply in your PC is not working.

Source of Information : Microsoft Press - Troubleshooting Windows 7 Inside Out