Do not follow the tutorial in that YouTube movie if you use a system install disk image. That tutorial is largely based on my manual, but it confuses a system install disk image with a installed system disk image. Hence the advice to not follow my directions to lock the system disk. A system install disk must be locked, a installed system disk should not be locked.
Which build of SheepShaver do you use? What kind of OS9 image do you use?
but when I quit SheepShaver, it gives me the blinking ? again.
When you quit
SheepShaver? You mean that it works, but after quitting it does not work when you launch SheepShaver again? If you use a system install disk image, did you install the system? If you used a installed system disk image, did you possibly remove that volume from the list? A system install disk image should be removed after installing the system (as described in my manual), a installed system disk image should of course not be removed (unless the system is copied to another volume).