Here is the tech sheet for this unit.
http://manuals.frigidaire.com/prodinfo_pdf/Anderson/240379014.pdf

First check that the compressor is running.
You can usually hear it also you should be able to feel it vibrating and it should be warm.

If compressor is running, remove the cover in the freezer so you can see the coils.
Check that the evaporator fan in the freezer is running.

If the coils are heavily iced/frosted over you probably have a defrost problem.

If there is no frost or just frost in one area (usually where the freon enters the coils). You have a sealed system problem.
This will be an expensive repair and often makes more sense to replace the unit.

Note: The above check must be done after the compressor has run a few hours. If you do it just after a defrost cycle then there will be no frost.