The Power Plant is out of order because you haven't found the machine part yet. It's hidden by the Rocket Grunt (who speaks in broken English) inside Cerulean Gym. When the power is back on, you'll be able to get the Poke Flute on the radio and wake up Snorlax. I believe you have to return to Lavender Town and get a Radio Card from the Radio Station, but you'll pass it on your way to Snorlax, if memory serves correctly.
Marriland - HGSS walk through