It probably is a stuck starter motor but I would just check that the engine is free to turn, pop a spanner on the front bottom pulley nut and give it a try.
I had a guy tell me his starter would not turn, when I investigated, it transpired that three months before, he had attempted to start his engine not realising that the compartment was partially flooded. This sucked a load of water into the air intake. Instead of dealing with it at once, he had just left it. I had to drive the pistons out with a hammer. A full rebuild was required on an engine less than two years old.
Ouch!