Does your key have a black chip on it? If so, your problem is an antitheft sytem failure. Inside the lock cylinder are 2 contacts that read the key. Each time you turn the key you are bending the wire that goes to these contacts. After a few thousand starts, the wire begins to break and won't read the key every time. Once it fails, you're locked out for 4 minutes before you can try it again. If it has failed once, it will fail again. Contact a tech to either bypass the system or replace the lock & key.