How to flash the GBA-MIDI-cable to recover from corrupted flash or get a newer firmware version:
- Grab a firmware update file from http://meuk.spritesserver.nl/gbamidi/
- Grab something that can play the MIDI file. I know Windows programs sometimes have trouble playing the file:
vanBasco's Karaoke Player usually works in that case.
- Hook up the GBA cable to a GBA and a MIDI port.
- Turn on the GBA, and at about the same time start playing the midi file to the cable
- Wait 30 seconds or so.
- If everything has worked, the GBA should boot into the firmware again. If not, try turning it off and on again.