My battery ran down on my 2005 Cadillac CTS because of non-use, sitting in my garage. I charged it up and it tests ok, but the car wont start and the lock out light is on the dash. If the battery is good what would be keeping the car from starting?

A loss of power triggers the Anti theft feature on you car. In some cases, if you lock the drivers door and unlock it with the key, you can reset or rearm the system.

Another method is to turn the key to the On position and leave it there 10 minutes. After 10 minutes, turn the key to attempt to start the car. If these 2 methods don't work, you may need to tow it to the dealer to have the Security reset.