New battery, new starter, new alternator, vehicle will not start

We drove twenty four hours from North Dakota to Texas, drove around Texas for about three weeks, finally one day we stopped, cut the truck off, went to start it back up, and all we got was click, click, click, click. Purchased a new starter, alternator, and battery, and it still would not start. Changed the negative battery terminal because of corrosion. It would began to crank, but it wouldn't turn over. Got the codes for camshaft sensor 1 and 2, so we changed those, and now we are back at the click, click, click.