The engine is locked up. Pull the cover off the PTO (end of the engine) take the spark plugs out, and see if you can turn it by hand.
If it turns... throw a towel over the sparkplug holes... and try to crank it again. (it may spray oil out)
If it does not turn... take the jet pump off the back. Sometimes if water gets into the pump bearings, and it sits... the pump locks up.
Le me know what you find.
We see this all the time here. A seller says... "All it needs is XXXX". But in reality, there are major issues. Lets hope we can figure it out, and it doesn't get expensive.