Engine will not turn over. lights, horn, everything else works, no clicks, no nothing, but it will not turn over.

You're describing a no rotation issue and not a no start issue correct? If you dont hear/feel the starter relay clicking, it eliminates everything in the circuit to that point meaning the ignition switch, Transmission Range Sensor (TRS) (you don't have a neutral start switch unless you have a rare manual transmission), ground input from the Powertrain Control Module (PCM) to the starter relay coil, and starter relay are good. Based on what you've said that leaves the primary battery cable from the battery to the starter, and the wire from the starter relay to the starter solenoid contact on the starter. Have you checked their continuity? One more voltage to check at contact 30 (input volts from battery to starter relay contacts) on the starter relay socket. Should see 12vdc all the time.

You should check the battery. The true test is a load test. Does jumping the battery using jumper cables make any difference? If it starts, change the battery. I take it to check the starter you jumpered the solenoid contact on the starter to the battery correct? Have you tried wiggling the battery cables as you turn the key? They can corrode and fail internally. Are the engine and chassy ground connections clean and tight?

When you turn the ignition key to start your car, voltage from the battery flows through the ignition switch to the Park/Neutral safety switch and/or brake pedal or clutch pedal safety switch (you have to push the pedal down before the circuit will complete) to the starter relay or solenoid. When the relay or solenoid is energized by voltage from the ignition switch circuit, it closes a contact that routes more power from the battery directly to the starter to crank the engine. The starter motor spins, pushes the starter drive gear to engage the flywheel and cranks the engine.

Low battery (Check battery voltage, recharge if low, or jump start with another vehicle or battery charger).
Loose or corroded battery cables (Inspect, clean and tighten BOTH ends of BOTH battery cables).
Bad starter relay wiring connections or ground connection (Inspect, clean, tighten wiring connections).
Bad starter relay/solenoid (Check for voltage at relay, if relay has voltage but there is no "click" when key is turned to start, replace relay).
Bad starter (Jump battery voltage direct to starter to see if it spins, or remove starter and have it bench tested at auto parts store).
Damaged starter drive or teeth on flywheel (Remove starter and inspect drive gear and flywheel teeth, replace damaged parts if necessary).
Bad ignition switch (Check to see if voltage reaches starter relay/solenoid when turn to start. If not, check for open P/N switch and brake or clutch pedal switch. Replace ignition switch if defective).
Open P/N safety switch, or open Brake Pedal Safety Switch (automatic transmission) or open Clutch Pedal Switch (manual transmission). Bypass switch with jumper wire to see if engine cranks, or use test light or voltmeter to check for voltage passing through switch when ignition is turned to start.
Engine seized due to bearing failure or internal damage (Use socket and long handle to see if engine can be turned by hand, if not engine is locked up).
Engine hydrolocked due to coolant leak from leaky head gasket (Use socket and wrench to see if engine rotates, remove spark plugs and see if coolant comes out or engine can not be cranked with plugs out).