Ok, this involves a few parts:
(If you already did the machine part mission, ignore this)
First head to the power plant, and talk to everyone until someone talks about a missing machine part (to be safe talk to everyone anyway), then leave, before you leave the security gaurd will get a call, and ask you to go catch the theif that's hiding in the cerulean gym, after you find him, he'll run away to the bridge leading to cerulean cape, when you find him there, go battle him. He'll tell you that the machine part is in the gym, behind an inner tube I beleive. Retrieve the machine part and give it back to one of the guys at the power plant, he'll thank you, and your radio will work.
After, go back to the snorlax, and go in front of him, go to your pokegear, go on the radio, and search until you found something that sounds like a lullaby.
snorlax will wake up and battle you.