Hi Jodie, I've just (fingers crossed) fixed a similar problem with our DE6544 (presumably quite similar model?), caused by not having cleaned the filters in over a year (oops, should have read the manual), like this:
Removed both filters in the bottom of the machine (and sponged out a large pool of smelly water).
Undid three screws and removed a round grey plastic thing.
Undid two more screws and removed the beige plastic thing with a pipe out of the top - this revealed a yellow impeller and an inlet/outlet hole with a green mesh filter inside. Cleaned away all muck, made sure the impeller could turn, reassembled, and so far it seems to be working...
Mike, October 2004