Will not start, when the key is turned there is nothing no clicking and the motor does not roll over. The headlights work fine and no change in brightness when the key is turned to crank. Starter was taken out and tested, checked ok, there is power to the starter but the power is lost when the key is turned to the crank position.

If nothing happens when you turn the ignition key to the "Start" position, it means that the starter motor doesn't turn over the engine. Most commonly this could be caused by a dead battery; read above How to check the battery

Clean the battery terminals and battery post , check battery is fully charged.

The battery terminal connections is loose or corroded.
Battery faulty or discharged, if the cable are clean and tight on the battery turn the key to the ON position and switch the headlights or windshield wipers. If they won't run then the battery is discharged.
Broken, loose or disconnected wires in the starting circuit.
Starter motor pinion jammed in flywheel ring gear.
Starter solenoid faulty, Starter motor faulty, Ignition switch faulty.

Lots of stuff !
#1 If you can ,try to start it in neutral.
#2 In park hold the key so start and have an assistant rap the
starter motor lightly with a bar or whatever(if that works the brushes
in the starter are going,starter time)
#3 turn on the headlights ,have your assistant watch,they should
be bright,then turn the key,if the lights stay bright,it's a fault of the
starter or key/ignition system. If the lights go dim or out it's just
a battery terminal connection.
A few things to try anyway,good luck.

If no movement of the engine happens at all, then please check the following:

1) Battery voltage. You should have 12.5 volts and over. Try turning on the headlights and cranking. If they dim considerably, then your battery is likely flat and may need charging/replacing.

2) Battery voltage is fine, but nothing happens: Is there a clicking when you turn the key? If so, then check the starter motor. It's likely failed.

3) Battery voltage is fine, but there is no clicking when I turn the key. Check voltage to the starter motor solenoid on the top of the motor. If it is receiving power when you turn the key to crank, yet not moving/engaging, then replace it.

4) Battery is fine, but no power to starter motor and/or solenoid. Check all battery connections, leads and connections to the motor and engine body.

You have a dead battery.
The procedure to fix it is as follows:
1) Charge battery.
2) check alternator belt tension. If loose, tighten or replace.
3) If still no start, replace battery.

The clicking sound is probably the relay that operates the starter motor, but the motor is not engaging. Chances are that this is one of 2 issues. Either you have a flat battery, so the relay clicks but there is not enough power to turn the starter motor or the motor its self is faulty.

An easy test for the battery is to simply open the door of the jeep look at the interior light and put on your headlights, if the interior light dims significantly and the headlights are dim, you have a flat battery!

If its the starter motor its self then begin by checking the connections on the back of the motor to make sure that they are clean and secure. While it's possible that you have a faulty relay, this is fairly unlikely and if the tests above don't give you any leads then you will need to start treating this as a starter motor failure

if you turn headlights on and turn key to start do you hear clicking? if so starter is possibly bad,lets trouble shoot your problem.suggest you check the fuses under hood in black box,make sure those are good. when you turn the key, you should hear at least a click or else the starter is not drawing current.try turning the headlights on and at same time turn the key and try to start, if lights go dim the starter is drawing current, does it click? if so then bad starter. if no noise at all,,still could be a bad starter.suggest that you remove the starter and have it checked out.also make sure the car is in park for sure before you do any of this. hope this helps!!

I think there is a microswitch on passengers side for roll over that isolates everything.

Try charging the battery or jumping the car, your alternator could be shot and not charging the battery.