Check the setting of the temperature control inside the refrigerator. Next check to ensure the coils on the back and at the bottom of the refrigerator are clean. Ensure that the refrigerator is not too close to the wall and has air space. Last check to make sure nothing has blocked the fan at the bottom of the refrigerator.
The fridge probably will not cool because it's air vents are clogged. Check the grill on the front near the floor to see if it is covered in dust. There will also be some sort of output on the back which may become clogged.
There is a chance of leakage of refrigerant gas leakage in the refrigerator. It can be fixed by refilling the gas of the refrigerator compressor. There is also a chance of leakage due to the damage of inner walls of refrigerator.
There a few obvious issues that could be at play. Your fridge has a compressor and id that is broken, it will not cool. If your freezer portion works but your fridge does not, it could be a faulty fan on the fridge side.