DIAGNOSIS The motor is running but the power isn't getting to the hammer mechanism. Most likely, the drive mode selector switch is stuck between settings, like between 'Hammer Drill' and 'Rotation Stop'.
FIX Unplug the tool. Firmly rotate the mode selector dial on the front all the way through its positions several times—from 'Hammer Drill' to 'Drill Only' to 'Rotation Stop' and back. Feel for a solid click at each stop. Plug it back in and try again with the selector fully clicked into 'Hammer Drill'.
IF THAT DIDN'T WORK The internal fork that engages the selector might be broken or the hammer cylinder is seized. That requires opening the gear housing to inspect. You'll need to remove the rear handle and gear housing screws.
HEADS UP Never force the selector dial while the tool is running. You'll strip the plastic fork. Always make sure it's fully seated in a mode before pulling the trigger.