I have a 1965 Mustang fastback with starting issues?
Sounds as if you either have a bum solenoid or the starter is seized.
Try bypassing the solenoid to see if the starter turns, just bump it, don't hold the bypass for any longer then a couple of seconds. You can do this by completing a circuit between both the big terminals on the solenoid, use a jumper cable.
If the starter fails to turn, try giving it a couple of good wacks with a hammer, this may loosen it enough to be able to start the car. I used to have to do this on an old 74' Torino I had until I could replace the starter.
If the starter still fails to turn, pop it off and take it to a major chain auto parts store, they can check it on a machine, if it is bad you are already where you need to be to get a new one! By the way, while your there, get a new solenoid too, last time I bought one they were only around 10 bucks.