Then loaded all the Preload data and... no sound at all, or, very weird: after power up every key just sounds once when you hit it, and then a deadly silence...
But I was finally able to solve this problem: My TEX went into some identity crisis and didn't know who she was anymore

This is how I've fixed it:
- Turn off the keyboard
- Hold buttons "-" and "Enter" (Self Check mode) while powering up
- Release the buttons when LCD is up
- Wait for the Self Check to complete
- Press the page menu button in the top right of the LCD
- Select "Select Keyboard"
- Now tag either 61, 76, 88 old or 88 new
- Click "OK"
Turn off keyboard, and on again. Problem solved!