I am assuming it is stone cold. First, is power reaching it? Check the individual fuse or breaker in the box supplying all the other storage heaters, particularly if the others in the house work OK. Overnight the power should come on around midnight. If the switch next to the heater is one with a light, does it come on at that time? If this switch has a fuse, have you checked that (usually 13Amp, if fitted)?