Circuit-breaker button on the multisocket? Damage to the plug into the computer power-supply-unit? Or the silly one, did you knock the switch of the power-supply-unit?

The first thing to do is plug something else into the multi-socket, just to be sure you have power to there. Change the power-lead (from multi-socket to CPU) for the one you're using and flick the PSU switch off-and-on.