Fridge not cooling...

This sounds like a problem with the defrost circuit. It is likely that the evaporator coil is clogged with ice due to the defrost heater not functioning. This can be caused by a failure of any one or more of the following components:

1) Defrost timer. Defrost timer may be "stuck" - failing to advance from a cooling cycle to a defrost cycle. May be found in the toe space of many fridges, but not all.

2) Defrost terminator. This is a thermal sensor that is secured to the refrigerant line close to the evaporator coil in / behind the freezer compartment. If this component fails to detect a rising temperature, it never allows the fridge to return to the cooling mode again.

3) Defroster Heating coil. This is a simple, relatively low wattage heater secured to or near the evaporator coil. It is powered through the defrost timer and shut off by the defrost terminator. If the coil is burned out or otherwise "open", it will not heat to melt ice buildup on the evaporator coil.

4) Fan. The fan is located near the evaporator coil. if the fan is unable move air from the freezer to the fridge, the compressor runs endlessly because cold air is not blown into the fridge compartment - where the thermostat is detecting a high temperature.

5) Condenser coil. If the condenser has a "furry jacket" it's long overdue for a cleaning. Gently vacuum lint / dust / dirt collected on the coil to increase efficiency. This is probably not the problem - but it probably needs to be done anyway.

Most of these steps will require hand tools, schematics (specific to your model), electrical test equipment, etc. Be careful to not use sharp instruments that may puncture refrigerant lines or electrical insulation. Allow the ice to defrost with the fridge powered off with the freezer door opened, and a pot of hot water inside, hair dryer directed at the coil, etc. Access to the evaporator coil is usually from the freezer compartment (back wall) and will require removal of any ice maker installed.