DIAGNOSIS The electronic overload protection has tripped. The clicking sound is the electronic switch attempting to reset. This happens when the tool is overloaded or overheats.
FIX Remove the battery from the drill. Wait 2-3 minutes for the tool's internal electronics to cool and reset. Inspect your screw or drill bit. Ensure it is not bound up in the material. Reinstall the battery. The tool should now operate normally.
IF THAT DIDN'T WORK The battery may have entered a low-voltage protection mode. Place the battery on its Ryobi charger. If the charger light flashes red/green, the battery is deeply discharged and needs a prolonged charge cycle before it will work again.
HEADS UP Continuous clicking without the motor engaging, even after a reset, indicates a potential failure of the trigger switch or motor controller. This requires professional service.