There is low or no water in shower cap.
Make sure pump is plugged in.
Make sure the outlet has not tripped the GFI or indoor breaker switch.
Check for a kink in the blue swivel hose.
Make sure blue swivel hose is firmly connected to the reservoir lid.
Unplug and replug the pump from the electrical outlet. Magnetic pumps sometimes need to be restarted after long periods of continuous operation.