In that case, I'm pretty sure HopCar nailed the problem: somebody flushed something that's jammed the pump...I'd bet 10-1 it's a d'd wet wipe.
In the future, be sure to warn your guests that
flushing ANYthing but body waste and the
toilet paper provided will jam the
toilet...that ANYthing else MUST go into the trash can (and provide ziplock bags for 'em to put it in).
You prob'ly should replace the intake and discharge impellers while you have the pump apart...or put a
rebuild kit that includes 'em in it if it's been at least 5 years since that was done.
--Peggie