Ignition switch will not turn off

Sounds like the relay in the starting motor circuit has failed, or a starting motor/solenoid problem - have them checked. This can also be caused by a problem in the ignition switch.

Could have faulty starter relay that provides crank signal voltage to starter when key is turned to start. Assume the no voltage to plugs or fuel pump performed when jumping the starter directly at the starter. Was the key turned to run position? Needs to be or no power to rest of system.

What about with the key in the on position -do the warning lights and gauges turn on? That would mean the ignition switch has power and can turn on.
Any theft alarm activated, immobilizing the car?
Won't turn over- you mean won't start or the starter won't spin the engine over? If it won't start, ignition spark or fuel problem. If the engine won't crank, problem is in the start circuit- from battery to starter, and from battery to ignition switch to starter. Park/neutral safety switch is in circuit between key switch and starter.

Sounds like the key may be old. Call gm dealer and they can pull up code to get u a new one if that is the original ignition. Only costs about $10 for new key.

Usually the security light means it can't read the chip in the key.. the little black chip at the base of the key.
Try using a spare key

you either could have a bad ignition switch or your ignition switch out of adjustment/loose causing not being in correct location

check the ground bar under the carpet by the drivers door sill it is probably corroded

I had the same problem.does your key spring back? If it doesn't take out your tumbler remove your starter ignition switch,held on by one srew,remove top and bottom plasticcouple screws,two screws on top to remove blinker switchs and lights.under tumbler casing two small screws hold shift cble remove that and in between starter switch and tumbler the rest off your ignition. remove this at the more than likely at the end the soft metal has broken so instead off it having a square end it's rounded so it can't turn your ignition you will have to replsce that unit .goodluck It has been a real pain in the *** trying ti figure it out.

although your ignition switch would have power go to the accessories, it still could not turn over. it happened to me, after a week of trouble shooting i went and found a starter button and spliced it into the ignition wires to see if that was the problem, lo and behold i turned the key on to run and pressed the button. and she fired right up.. if you know anyone with mechanical skill. its pretty simple to set up. took me 10 min to do.

good luck

Hello!

Sounds like a stuck ignition relay. 
Try tapping with something ******* the ignition switch when this happens, see if it helps.
If it does consider replacing the ignition switch.

Hope this helps!