Car wont register key coming out of ignition

[mpiacent]

ok so yesterday i turn off my car take the key out all is normal open the door and the car starts doing the beeping that happens when you leave your key in the ignition and all of the cars lights stay on ... i tried turning the car back on and then off and removing the key several times and had no luck. eventually i had to just unplug the battery so that the car wouldnt die. any ideas on how to fix this anyone? any help would be greatly appreciated its a 02 gp gt