Hi Amigaharry2 and Jacadcaps!

Thanks a lot for your advice, some progress!

I used a regular PC keyboard and booted the G5 while holding "Windows" + Alt + O + F. The screen, as usual, "switched off" after some seconds. But I noticed that pressing NumLock would switch the LED on/off (as expected). So I "blindly" typed the commands that you suggested and the G5 indeed resetted... So I was in OF! Only without an image on screen...

I tried the same procedure but typed "mac-boot" and the G5 booted into MorphOS!

So, it seems that OF doesn't display on screen, even after resetting everything.
Should I have mentioned that my screen is one of these 30" Cinema HD Displays?

Besides the lack of display, the boot behaves as last week: MorphOS doesn't boot automagically, I must go into OF and type "mac-boot"...

What do you think that I could I try to fix either (or both!) of these problems?

Cheers!