Wireless Drum Receiver
The wireless drum receiver is the primary device used to sync the drums to the PS3 and is one of the most common culprits when the drums do not sync. Verify that the device is powered and connected to the PS3 properly.
Faulty Drum Set
Confirm the drums have working batteries and are operational. If the lights on the front panel are active, this indicates the drums are powered. Testing the drums on another PS3 also might give you a better idea of what is not working.
Wireless Interference
Interference from other wireless peripherals can prevent the drums from syncing. Disabling them or moving them farther away from the wireless drum receiver might remedy the issue.