There is a recall on Whirlpool dehumidifiers that may cover your unit, the website lists serial numbers of units on the recall list.
Dehumidifier Recall FAQs
I assume from your question that at least the fan is running. There are many reasons why a dehumidifier is not removing water from the air. Most likely is accumulation of dust and pet hair that restricts the air flow. If you can, unplug it, take off the covers and vacuum out all the dirt from the evaporator and condenser (little radiator like parts). This website has some good blow up pictures of how it is put together and part nomenclature:
WHIRLPOOL DEHUMIDIFIER Parts Model AD25J3 SearsPartsDirect
If the air flow is restricted, the compressor has to work harder to the point that the overload gets tripped. It may or may not be resettable; it is part #10 in the diagram on this page:
http www searspartsdirect com Whirlpool Dehumidifier Parts Model AD25J3...
If you do take the covers off, check that the fan turns freely and you may want to add a drop of oil to each end of the motor if there is a place to oil it. Light oil like sewing machine oil or light engine oil will do.
You cannot really tell if the compressor is working with all of the covers on; and I cannot recommend plugging it in with covers removed because there may be open electrical connections that you do not want to touch. However if the compressor is running, the outlet tube will get hot; that is the one that goes to the condenser [radiator like bundle of tubes nearest the fan] [it may get too hot to touch]. The evaporator [bundle of tubes farthest from the fan] should start to get cold where the tiny little tube from the condenser joins. If neither is happening and you are sure the compressor is running, it is out of refrigerant [freon] and may or may not be worth fixing. If the evaporator ices up [gets covered with frost] it may be low on refrigerant indicating a leak; again it may not be worth fixing.