Originally Posted by KiwiJochen

Try following:

1. Use V21 Os. This has a different EEPROM memory map layout. Maybe it will kick the nav into life.

2. If you get it going with V21, then check the boot mode and try reloading V31.
NOTE: BEFORE you use V31, check the OS disc for errors. Measure then with a disc checking program! Do a surface scan!