Hi there, I'm still new to the old macs, but it could be that it's defaulting to the wrong default drive?

I believe resetting the pram is the same one the older macs -

cmd+option+p+r

And I'm pretty sure you can tell it to boot from a particular SCSI with cmd+option+shift+del+the number of the drive, which would be 0 for the internal? So

Cmd+option+shift+del+0?

Maybe worth a shot until someone more knowledgeable sees this