-Check ventilation around the fridge. You need approximately 20mm at sides and top with 100mm at the rear.  If the fridge is in a cupboard or behind a fridge door you will need to have "Chimney effect ventilation"  This is where there is a vent at the bottom of the cupboard to let the fresh air in and a vent at the top of the cupboard to let the hot air escape. 

 -Check compressor definitely comes ON

-Check what temperature the fridge is set on.  5 is the coldest.