It has a decompression lever I believe?
If so decompress it and turn it over by hand to ensure the motor
if free. Once you know its not locked up the next step is electrical
connections, take them all loose one at a time and clean them with a wire brush and put a light coat of grease on them and reconnect them.
Once that is done if that doesn't fix it, jumper the solenoid directly, you know the screwdriver trick, if that doesn't work, I'd then pull the starter.
Often times the problem is with the ground wire and people forget to check the ground.