Some things to try if your ignition lock cylinder won't turn:

1: Move the steering wheel back and forth while turning the key. If the wheel is hard aginst the stop, it can jam the lock cylinder.

2: Try another key. Your key can wear over time. The dealer can make up a new key for you when given the VIN.

3: Lubricate the lock. A pin may be stuck. Use graphite, or silicone or teflon spray. Don't use WD-40 as this dries up and leaves a sticky residue.

4: Turn the key to the accessory position (if you can) and push in the pin on the housing to pop the lock cylinder out. You can get a locksmith to repair it or buy a replacement.

5: If you can't turn the key after trying all the above, hit the retaining pin with a hammer and punch and it will sometimes come out even with the key not in the accessory position. Or you can drill the lock out.

6: Call a locksmith.

Hope this helps.