2001 Chevy Prizm Ignition switch

Recently, the ignition switch will hang up and I cannot turn the car on. This happens with all of the 4 keys that I have, so I don't think it's a key issue. Turning the steering wheel slightly, one way or the other doesn't seem to help. Any ideas as to what is hanging up the ignition switch? When the switch does release, it acts smoothly and the car starts right up. Sometimes, removing and re-inserting the key will cause the switch to release.