ballast issue

I have a Mastercraft X5, which has rear ballast. I have been experiancing problems were the bag will not fill, and in fact does not even sound like the pump is turning on. Now the issue is when I switch it to evacuate the water, it does turn on. So basically it will push out but not intake the water. Any ideas before I pay some god awfull amount of dough to find out it was a smiple at home fix problem? Thanks