If the steering lock is on you might have to release the pressure on it before you can turn the key. Even though you won't be able to turn the steering wheel you can still turn it enough to take the pressure off the steering lock.
If that is not your problem then persistence in turning the key sometimes works. If all that fails you might need to call a locksmith because it is very difficult to remove the barrel if you can't turn the key.
Apologies for adding on so longer after post,just came upon it.
check to see if the lock barrel is protruding by a couple of mm.
If so use a slim strip of metal(I use the long strip that comes from either side of some wiper blades),slide the strip in between the barrel and the housing while pushing on the end of the barrel where the key would go,as you insert the strip approx 10mm slide it clockwise a little and the lock should disengage,the barrel should click inwards to flush with housing.
Hold it in this position and slip the key in,it should now turn.
Note:if you remove the key it will lock again,just repeat the process.
Often the car will now be able to start if it was just the lock jamming,helps you get it off the street and home to do the work.
Hope this helps all with this lock dilemma.
oops nearly forgot...first remove the plastic ring with the enable loop that is on the front of the ignition,so that you can see and do the above.
....now the barrel can be removed by pushing a small pin type object into top of housing to release it while the key is in the on position.
Don't forget you will need to hold the enable housing next to the key to start the engine if you can now turn the ignition to start.
