That's a tough call. It could be something as simple as a bit too much corrosion in your battery cable, most likely near the clamp on the positive cable. If it were me, I would jump the starter directly. This involves hooking the jumper cables from your battery, or another good one, to the starter. The positive cable goes to your solenoid (where your car's battery cable connects) and the neg. jumper cable goes to ground somewhere (frame). If your starter is okay, it should engage when everything is connected (watch your eyes for sparks). If it engages, you will know it's not the starter or your battery and may be cables or ignition or tranny.... Somebody correct me on jumping the starter, it's a bit hard to explain clearly.