igntion key cylinder lockup

[Cobraman1024]

basically has anyone had a problem with their "theft system" malfunctioning because of a bad ignition key cylinder?? this is the second time in 6 months that i'm having to replace the key lock cylinder. the first time, the car would not start and the "theft" light came on; successive times the key either wouldn't turn into the "start" position or it would but the car would crank forever but no start. normally that theft system activates when the car thinks you've put the wrong key in the ignition. currently (along with the DTC's in the next post) it seems as though my key cylinder has locked itself out of the "start" postion. it will turn just slightly into it--------enough to cause the stereo and other accessories to blank out but the key is somehow not allowed to fully turn into the start position to allow my car to even crank. i've cleaned the battery terminals and the terminal that connects the positive battery cable to the starter. any other ideas???