Battery is dead......that is why you had to use the key to unlock the door.
Once the key was inserted and turned in the ignition, you found no response.
The system will not allow the key to be turned back to the lock (and remove) position with a dead battery.
If you attach a jumper and restore power, the key will then turn back to lock and you can remove it........or, with jumper attached, start the car.......you decide.
For those wondering about this, OP also started this thread. We may be dealing with a flood damaged car. I'd involve the insurance company. I'd also suggest taking it to a dealer to be evaluated. Flood damage is a serious thing and can have lasting problems.I brought a mechanic and is telling me the the water has entered the body control module and airbags control board therefore the key can't turn to lock position unless i change it.