A model number may help others help you.

First confirm that it is a sealed system problem.
You can usually hear the compressor but you should also be able to feel it vibrating and it should be warm.
It should be on except when the unit is in a defrost cycle then the fans and the compressor will be off.

If it is on, remove the cover inside the freezer so you can inspect the evaporator coil.
If there is frost in just one area (usually where the freon enters the coils) then you are probably low on freon. The operative word here is probably.
If it is low freon there is no use getting the unit recharged until the leak is found and repaired.

If there is no frost the either you are out of freon or the compressor is shot.
The only way to tell for sure is to check with a set of gauges re: you need a pro.

It does sound like a sealed system problem and will be an expensive repair with no guarantee of a long term fix. In most cases it makes more sense to put thos dollars towards a new unit.