I'm assuming you tried unplugging and re-plugin in the modem, put if not give it a shot.
Check if your modem has an on switch, and make sure it's in the on position. Double check the outlet, try a different one, or pug some other device into this one. lastly it could be a problem with the power cord, try unplugging it and wiggle it at both ends, check the line, and you can try replacing it. But at this point I would get a new modem or contact your ISP if you are renting it.