This sounds like a damaged, loose, or dirty internal SD card. You can try removing the SD card cleaning it and then reinserting it. This has worked for people in the past. If that doesn't work you could try a replacement SD card. You'll need to get one specially for the Firehawk FX from a Line6 parts supplier because there is no way to flash the firmware to the SD with it in the unit and I'm not aware of any PC software that can write the firmware to it directly.