External devices such as external modems and printers and scanners have power cords as well.
Plugs can come loose so make sure everything is connected.
If your computer plugs into a power strip, check to see if the power switch has a switch of it's own. Make sure the power switch is on the on position and the lights are functioning. If nothing works check to see if there is a problem with the outlet. Plug it in to another outlet that you know works. Keep the software up to date.