I have a 2001DeVille with 100,000km and now the key will not turn the switch at all. Any suggestions.

Turn the steering wheel back & forth while trying gently to turn the key.

I tried that gem. We sprayed lube, made sure the batt was charged too. At first the key wouldn't even go in the slot but now it does. When the key is in the dome lights come on as well as the seat adjustment all like normal.

try spraying wd40 in there and put the key in and out a bunch of times