I had this problem one day after work.... I had to call a lock smith to insert a new key cylinder $150.00. He says this go out all the time.
I watched what he did; he made a copy of my key; stuck it into the cylinder and bang on the key with the end of screwdriver and force the key to turn.
2001 WJ Black Limited 4.7 - 3"(2BB"+1"UC) lift, IRO track bar, DT shocks, 245x75x17MTs (31.7")