I suspect the impeller is firmly stuck to the inside of its housing, which happens quite a bit because waste is sticky and it rarely occurs to many people to rinse out the system after using it. The pump tries, but shuts down to prevent burning out the motor when the impeller can't move. Rinsing out the pump and replacing the impeller will prob'ly solve your immediate problem, but it won't prevent it happening again to your existing pump or any brand of new impeller pump if the pump isn't rinsed out before the boat sits. Few people ever even do that when prepping the boat for winter layup.
An electric diaphragm pump will save you from yourself in more ways than one, because there's no impeller to get stuck or be "fried" when allowed to run dry because diaphragm pumps can run dry without harm. They cost a bit more than impeller macerators, but it only takes a couple of new impellers to make up that difference. The Dometic/SeaLand "T-Series" pump is the best on the market:
T series waste discharge pump I had one on one of my own boats that was 11 yrs old when I sold the boat and still working as well as it did when it was new.