You will need to provide more information. Was this sudden or gradual, Is compressor and condenser fan running, what are storage comp. temps, etc. There are too many variables that need to be narrowed down. Check the condenser coils for dust build up if everything is running and clean them if they are clogged, also feel the suction side tube about 6 inches from compressor, it should feel cold and the line to condenser should be hot. If this is not the case then it's either a sealed system problem or a control board issue. Either way please provide more info.