this sounds a bit crazy?.. but does the pump make the water you put in the filter housing move at all?
a friend had a similar problem with an above ground pump that worked fine before shutting down for winter, then when trying to re-open the pool, the pump would not prime.. after trying everything possible with hose feeding into the inlet directly.. there was no output from the pump, despite the housing being full.. stripping the pump revealed the impellor had split in two.. the body of the blades rotating, but the front end had split away.. glued and screwed together again, it worked, but not as it should.. new pump was the only answer.. how and why it broke???.. ever fouund the answer..
you coud try to prime with a hose into the pool inlet.. or check for foreign objects [ frogs, dead critters in the input port??