I currently have a 4 piece concrete fountain (you know, one that has a chubby woman on top holding a basket where the water comes out) The only time I had water not coming straight up and into her basket was when the pump hose was kinked so flow was restricted. My homespun (I am famous for this) hunch is that you have an obstruction to the flow somehow. Run a coathanger or something down where the water is supposed to come out. Maybe a marble got stuck inside the fountain?
Not being able to see the fountain makes diagnosis difficult, but it sure seems like a flow issue, not a plug issue.