Diagnosis
The unit is likely frozen up or the air filters are completely blocked, preventing airflow over the cold coils.
How to Fix It
Turn it off. Check the two foam filters (one on each side). Remove and rinse them under warm water until clean, squeeze out excess water, and let them air dry completely before reinstalling. While filters are out, look through the grilles—if you see a block of ice on the coils, let the unit thaw for 6-8 hours.
If That Didn't Work
Your space may be too large, too open, or have a constant source of new moisture overwhelming it. The "120-pint" rating is under ideal lab conditions. In a cool, open basement, actual output can be half that. Contain the space with doors or add a second unit.
Heads Up
Never run it without the filters. Dust coating the evaporator coil is the most common cause of permanent performance loss, and it's not covered under warranty.