What are the symptoms of it not working? Is it possible that the optical drive inside has failed? Does it accept discs and spin normally? Do you hear the fan running? Do you get video and or audio? Check the cables to your TV and controller. Try a different controller.
Make sure that the plug of the playstation 2 is firmly and exactly plugged into your outlet. Check the voltage of your ps2. most ps2 are 100 / 120 watts.
You didn't say anything specific, so let's start general as well. Check that your power cable is in one piece and plugged in to an outlet you know works. If it won't turn on with that much done, you may want to look into replacing it. If it turns on though, your discs may be scratched, which easier to solve.