The fact that it doesn't even crank on occasion is an indication that it is likely nothing to do with the ignition circuit.

Is you engine grounding wire/s bolted down solid (ground strap on transmission).
Starter motor bolted on solid?
Assuming that you do in fact hear the starter solenoid click but no crank means it's either a power to the starter motor issue (either the power feed where it bolts to the starter solenoid or the power link between starter solenoid and starter motor as power is passed through), or a grounding issue, or an actual starter motor fault.

Regardless of any other problems this is the first step. Report back.