Diagnosis
The room's humidity is likely already low, or the humidity sensor is out of calibration, making the unit think it's done.
How to Fix It
First, verify the room actually needs dehumidifying. Use a separate hygrometer. If it's truly damp, force a test. Set the unit to 'Continuous' mode (the water drop icon) and the fan to 'High'. This bypasses the humidistat. It should start pulling water within an hour in a damp space.
If That Didn't Work
Check for a blocked air path. Vacuum the intake and exhaust grilles thoroughly. If airflow is restricted, the coil won't get cold enough to condense water. Also, ensure the bucket is clicked fully into place—the unit won't run if the bucket sensor isn't engaged.
Heads Up
In 'Continuous' mode, it will run until you turn it off or the bucket is full. Monitor it to prevent overflow. If it still pulls no water in 'Continuous' mode in a verified damp room, the refrigerant system may have failed.