NB Before proceeding, note that I am sticking with OS 9 for legacy/compatibility reasons with an important musical collaborator. So going to OS 10 completely is not currently an option. I have been using a G4 AGP Graphics, OS 9.1, CPU 400MHz Bus 100MHz, with two Seagate Barracuda 7200 drives, with Digital Performer 2.7 on it (that legacy app). I acquired a G4 Digital Audio, with OS 10.3, CUP 733MHz, Bus 133MHz, with an IBM deskstar 7200 in it. So I thought I would simply swap the drive bays, but the G4 Digital audio wont boot properly. I get the opening chord, and then the flashing alternating OS 9 logo and question mark ? I wonder, does it somehow need to start from scratch, with a different OS ? By way of experiment, I put one of the OS 9 drives in the upper bay of the 10.3 drive, and it was recognised and readable under OS 10. So I changed the default start up options to the OS 9 drive, and rebooted, but I got the same flashing question mark for a few seconds, then it went back to OS 10 by itself ?