Sounds like the dying happened over a period of time so I'm thinking the motor bearings ground up. Could be an easy and cheap fix if the blasted things aren't rusted on the motor shaft like the one I'm working on. If the motor looks like it is clean with little or no obvious weathering then I'd pull it apart and explore. If you can separate the motor from the pump housing, first step, without snapping screws because of rust, that's a good sign. At this point you have nothing to lose. The motor I'm working on is so badly weathered I started using a 20 ton press to get the back bearing off and quit before I squashed the shaft. Letting liquid wrench work for a few days before trying again. I unseized it enough to check that the electrical is fine so now it's a just (ha!) a bearing replacement issue.
Al
PS: Moral of this story....if you can cover a pump to keep the weather off it, do it. Mine is in a poolhouse, 9 years old, and looks and runs like new.