Before doing anything major I'd try switching to the backup firmware. The AVIC headunits have to firmware copies. So whenever the firmware is updated, the older one is preserved. The one that gets executed at boot time is controlled by whether PRG.FLG exists. You can force it to use the backup version using that file.
Boot into (Super)Testmode. Navigate to the USER directory. If a file named PRG.FLG exists, delete it. (it is just an empty file).
If PRG.FLG doesn't exist, add one by creating an empty file on your PC, copy it to the TestMode SD, then boot into TestMode and copy PRG.FLG from the SD to USER. If all that sounds complicated to you, here is a script that will add PRG.FLG for you. Just download and unzip PRG-FLG-Script, copy the 3 files to a smallish SD (less than 8GB) and insert it into your headunit. It should reboot into Testmode and run the script. If it doesn't, you may need to cycle the power on the headunit.
However, you didn't say what caused this problem. I hope you didn't cause the problem yourself by installing Condi's Hackmode or some other hack. If so, you might of corrupted the firmware beyond repair - or need a complete refresh.
PRG-FLG-Script.zip