Here are your parts
Replacement parts for PLRU1777DSO models | AppliancePartsPros.com

Here is the wiring diagram
http://manuals.frigidaire.com/p...df/StCloud/297005300.pdf

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

If it is on check that the compressor/condenser fan is running.

Check that the evaporator/fridge fan is running.

If all OK, remove the cover inside the fridge so you can inspect the evaporator coils.

If they are heavily frosted/iced over then you have a defrost problem.

If there is no frost or just frost in one area, usually where the freon enters the coils, then you have a sealed system problem.
This will be an expensive repair as you will need a pro and often it makes more sense to put those dollars towards a new unit.