What pump is it?(psi?)
Where have you mounted your pump?(mount as low to the floor as possible as some pumps can struggle to draw the water if higher than the tank outlet)
Have you disconnected the hosereel?does it pump when you disconnect the hose reel?
Definitely not got any kinks?
Are you using stop hoselocks?(dont as they can be an arse)
To be honest mate, sounds like an air lock...(pumps working but sounds more hollow?)
Disconnect the reel and turn pump on full blast.give it a min and it should kick in.
Edit : or suck the hose to help the pump draw the water until it kicks in.
Hope its one of these..