Whether or not a dehumidifier can be repaired depends on the dehumidifier and the particular problem it has. Humidity setting, water buckets, lack of airflow, dirty air filters and frost on the dehumidifier coils are all common problems.
If the humidifier is not running even in humid air, first check its humidity setting and adjust accordingly. Make sure the water bucket is empty and that it is properly placed inside the unit so that it makes contact with the bucket sensor switch. Also check the air filters, cleaning or replacing them when needed. If there is no air blowing out from the dehumidifier when it is running, check the motor of its fan to make sure it does not need replacement.
Frost on the coils usually means that the air in the room is too cold, which can mean any temperature below 65 degrees Fahrenheit for most humidifiers. Frost problems can often be resolved simply by warming up the room or even just raising the humidifier to a higher surface.