The "locking up" of audio system happened to one of my neighbors 2002 Camry as well. The SEC displayed seems to be a security issue and often interacts with Auto Theft System/Security (ATS) such as the Alarm.
Disable your audio system and ATS wirings, insert your ignition key and turn it to ON position and then OFF. Reconnect your audio system only (not your ATS) and then turn your ignition to ON. If the audio works, reconnect your ATS. It worked on my neighbor's car.
If still not successfull, then take your car to an audio/alarm/tint store and they may reset it for a very nominal charge (far less than dealers).