My ignition switch will not turn.

See if your steering was under tension. Try leaning into turning it one way and turning the key. Then the other way. really grasp and turn leaning into it as you try to turn the key. The brake pedal circuits in the late 90's actuate a release you can hear, or they may need a fuse replaced. The emergency procedure for the cars I worked on, was apply the brake turn against the wheel, turn the key, pull gearshift down a click, retry. Get it unlocked that way, pull down into neutral, and start in neutral. please try , then report findings. A GM car doing this, may be parked on an incline and an uneven surface. With normal wear, it may take some coaxing. to get the forces acting against it relaxed.

Not saying you need an undue amount of force. But rocking the car forward and back comes to mind. Tapping on the column lock housing while trying to turn the key, then even a shot of lockease. The works can get frozen. Then fiddle.

Use the tilt steering level to jar it loose.

Lever

Thanks for all the help. I tried everything except the fuse. However, none of them worked. Dannyl, I cannot put the car into any gear to try and turn the key. I can use the steering lever to move the steering wheel up and down. It just will not turn right or left. There is no play in the ignition switch. And very little in the steering column. It has been too warm to have anything frozen. Thanks, Ken

The lock cylinder cannot turn. Because the key does not match. Something has occurred inside the lock cylinder. The wear, or the need for lockease. But the fuse, if your system is like the ones I had everyday, the release acuates when depressing the brake. You would think 110 years of having vehicles on the road would have every driver stepping on his service brake before anything. but no, they have to add that system. definitely going to need that to work before going back to the key and cylinder issue. I had a GM car do this once and the guys rocked it fore and aft and tapped the lock housing. Newer stuff probably is all junk, and you should take it to the locksmith to have the worn cylinder parts looked at. of course your cadillac dealer should be consulted, They have an auto van for roadside help. their techs take turns saving cadillacs on the weekends. at least that was how it once was.

My 2005 Deville experienced the same issue. My local Cadillac dealer told me this was a common problem for 2001 to 2005 Devilles and the only solution was to replace the ignition switch which they did. In addition, I was told in order for the ignition switch key to operate the trunk, that lock mechanism had to be replaced. Total bill was $ 1300. I think I was conned but I had to pay to get the vehicle released to me.