Snorlax won't wake up in HeartGold

You need the Poke Flute channel on the radio. That means fixing the Power Plant first - find the missing machine part and bring it back to the manager - and then the Kanto stations start working. Stand next to Snorlax, open the Pokegear, tune the radio to the Poke Flute channel, then talk to it. Save before you wake it, you only get the one.