Detail would help - can you hear the pump running when operating the switch? If not, have you checked the fuses? If the pumps running, try pulling the flexible black pipe off the pump when running, and advise if any water comes out (if it does, you're going to get wet)!
Final daft question, confirm you have fluid in the reservoir and it (the reservoir) is clean of muck - the inlet at low level inside the tank may be clogged.
Final daft question, confirm you have fluid in the reservoir and it (the reservoir) is clean of muck - the inlet at low level inside the tank may be clogged.