1. No battery - Dead battery.
2. Stater solenoid, shoulda rapped it a bit with a tire iron to see if it could be engaged.
3. Did the headlights work? If so it's probably the starter solenoid or key switch.
Verify you have +12 on the purple wire when the key switch is on at the starter. To do this you need to clip lead a wire to the terminal and get out from under the car when the key is turned to the start position. If it reads +12 then the solenoid is shot and it's not the keyswitch or wiring.
Assuming your big fat red battery cable is good to the other terminal on the starter.
And check the ground wire from the battery to the turbo bracket front of the head area too.
Although my car started and cranked without that wire being on there very tight.