i just tried to install the Sierra GM and I got the following message: MacOS could not be installed on your computer An internal error has occurred Quit the installer to restart your computer and try again When I do this, it automatically tries to install the Sierra GM again, which again fails. I tried to short circuit this process and held down the option key at startup but I am not given an option for startup disks. So I'm stuck and can't use my machine for work tomorrow. Can anyone help me? Edit: I can access disk utility once the install fails and before the restart. It says that the HD on my machine is damaged and can't be repaired. This is odd since I ran disk utility just the other day and it was fine. I can also access terminal.