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The first thing I would do, is use a digital multimeter across battery posts, everything off, take reading, the generic spec for a full charge is around 12.6 volts. If your reading is much less, you need to charge the battery. With meter leads touching battery posts, have a helper turn the key to crank, if complete circuit, the reading shouldn't drop below 9.6 volts, if it drops down close to zero, that's not going to work. Another thing that might happen, is not much drop at all, that usually means an open starter circuit, somewhere.What about battery connections?
See the starter relay, if you unplug the relay and use a jumper wire between terminal 30 and 87, the starter motor should crank, if voltage--ground and starter motor are ok. If you try that, make sure tranny is in park or neutral and parking brake is set. Safety is your responsibility.
You can remove the starter, lay it on the ground, hook up jumper cables properly from battery to starter motor, it should kick out the drive gear and spin. Some of the national brand auto stores will test your starter motor for free, I believe, if you take it to them.
Check your charging system. I could go on and on, but, my post is already too long. Just trying to help.