Oldsmobile/Buick Repair: 99 cutlas, gm dealership, key cylinder

Question
the key won't turn,it was fine this morning,and now it's not.what might be the problem?

Answer
Hi
First try the other key  if you have it, see if it works. IF NOT AVALIBLE, and if the 4th digit of your car is an "N" I would take the title, registration,  proof of insurance and your drivers license to your local GM Dealership.
Have them cut a NEW key from the VIN.
DO NOT copy cut the key.
The sharp crisp edges of a new key cause the worn tumblers inside the key cylinder to "drop" farther, which will in turn let you rotate the key.
I have seen this ALOT of times. ALOT.
I hope this helps.
Just advice from experience.
Good luck
Pawl