bloody bio-wheels... what system is it in? if it's in a penguin, odds are the filter pad is clogged. Mine clogged weekly until i took it out and shoved two aquaclear sponges in it. If you see water flowing out over the intake tube, it's surely clogged. Take some water out of the tank and rinse the filter cartridge real well. Rub the floss hard, both against your palm and back against the plastc frame.
if it's not a penguin, or if it IS and there's no water flowing out over the intake, the bio-wheel's mounting probably needs cleaning. On penguin models, there's a white rod that goes into a green cuff, and the green cuff snaps into the frame. Clean the frame, inside and outside of the cuff, and the white rod. (to get inside the cuff, twist up a peice of paper or use the stick of a Q-tip) If it's not a penguin, clean the parts of the axle that rest in the cradle, as well as the cradles. If that doesnt do it, clean your impeller and intake tube, the flow might be restricted by grime to the point where there's not enough water flow to spin the wheel. And, from now on, buy aquaclear filters. They're just so much better, in my experience.
Give me a plain ole tank and filter any day 
