DIAGNOSIS The motor is getting power but the mechanical connection to the chuck is broken. This is almost always a stripped planetary gear in the transmission.
FIX Replace the transmission assembly. It's a single module.
- Remove the battery.
- Take out the long screws from the gear housing.
- Separate the motor/trigger housing from the transmission housing.
- The old transmission lifts out; drop the new one in.
- Reassemble. No gear alignment needed.
IF THAT DIDN'T WORK If the transmission is new and it still just clicks, the issue is upstream. The motor armature might have failed or the trigger/switch assembly is faulty and not sending full power.
HEADS UP Don't run the drill in this state. The clicking is metal teeth grinding. Continuing will turn a simple gear replacement into a need to replace the entire gearbox shell and possibly the motor.