On pluging on the main AC pluf, there is not

do you have the cord plugged into the computer? is there a switch on the back near the power supply? if so, is it on? is the large connector from the power supply tightly latched to the mother board? (unplug the computer before you check this!) any fans running? plug a lamp into the outlet and see if it has power! could be a popped breaker, or blown fuse.if you feel confident of your skill, remove the power supply, open it up and see if it has a fuse that may be blown. if so, replace it with a fuse of the same type (size & amperage). if the fuse was blown, and you re-install the power supply and it blows again, then you have a problem (probably) with the power supply, and if cost effective, it needs replacing! get a compatible power supply with a higher power rating, if you can! more power for your peripherals!
good luck!