It is possible that the key is very worn or the tumblers inside the lock are worn. you can get the dealer to cut you a new key with your VIN #. If that does not work, you will have to remove the actual lock. Here is what I found here "On models equipped with airbags, disarm airbag system as outlined under Technician Safety Information.
On models less airbags, disconnect battery ground cable.
On models with coded audio anti-theft systems, remove steering wheel, if necessary, steering column garnish, if equipped, upper and lower covers.
Disconnect electrical connectors from ignition switch.
Now if you can not more the key to the ACC position you will have to remove the whole unit. That means to remove the trim and there are two bolts that secure the unit. Drill those out and get a new unit. Not very expensive and available by using Google. The new unit will come with the two new bolts. that will shear when they reach the proper torque. Anyhow, I hope that this will get you started.
Oh and one more thing. Make sure that you are having the right key. Nothing worse than trying to start your car with the wrong key....;-) Good Luck