You can make a jumper wire, remove the starter relay and put it into the wire terminals to force the starter to crank. With the key on and the starter manually being forced to crank it should start. If it does not then you are likely having another issue.
The ECU controls the starter, not the key. When you turn the key to start it the ECU reads this and then decides if it will allow the starter to turn. If you have having sentry/security key issues then the ECU will not allow a start. It will also not start even if you bypass the starter relay and force the engine to turn over.
Try making a jumper and touching it across the connections where the starter relay would go. I don't remember which pins it is but there is a diagram on the relay that if you can decode will tell you what two you need to jump across.
Do you have any other issues? Odd lights on the dash? Is the small red LED lit on the lower left of the cluster? Do you have a code reader with you?
I had a similiar, but maybe totally different issue that lead to no start, check fuse 14 in the cabin fuse box and see if its blown - if it is the ECU and TCM get no power and the vehicle will not start, however if this fuse is blown you will have extra lights on the cluster than normal.
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