The key has to do with the car that doesnt want to turn on?

It could be a failed key !! haveyou tried your spare key ? if not it could be the EIS or ESL (electronic steering lock )

could possibly be a worn key not pushing the pins

Could be the Neutral Safety Switch.
Turn the key to the position before actually turning the engine over then put the car in neutral then turn the key all of the way and see if that works.

Do you have another Ignition key? Those keys have a chip inside them. You can try un hooking your battery for a little while if it doesnt start with a different key. If that doesnt help you try turning the key on and off ten times as fast as you can.

Make sure the steering wheel doesnt have preasure on the lock, turn wheel to the left and to the right with a little force while trying to turn the key, this happens alot, if this doesnt help then you may have a bad worn key or the switch is broke or worn,try wiggleing the key in the ignition and turning at the same time to get it to turn good luck hope this helps you.

I would check the ignition switch, these are prone to key and barrel wear, Sounds silly but if you have another key try that as a newer,less worn profile key can sometimes help with a solution

as long as it doesnt drive off into the sunset without the key in it, i wouldn't worry too much about it

try resetting the security system, follow this procedure.
PASS LOCK RESET GM CARS 1999 UP
1) Put the key in the ignition and turn to the "ON" position. Leave it that way for 10 minutes. After 10 minutes turn the key and take it out. Repeat this process (2) more times (3 times, 30 minutes total) This should reset the passlock system to recognize your key.

no shims are required, check your electrical connections at the starter