Probable causes are either a blockage in water outlet pipe leading to the pump or pump has packed up. Two things to look for. Is the small filter still attached to end of water pipe when in resevoir? If that's missing something could have been sucked towards pump. If filter secure can you here pump running? You'll probably need someone to check out the pump.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vacuum cleaners.