Volume contains macOS or OS X installation media. Quit the installer and restart to try again
I just bought a refurbished iMac mid2010 and im trying to update my system to the OS high sierra, but when it restarts to install i am stuck with the message "Volume contains macOS or OS X installation media. Quit the installer and restart to try again" i tryed to just restart to my old startup disk but now when it restarts it just goes straight to the MacOS Utilities page( time machine backup, reinstall OS X, online help and disk utilities.)
I dont know what to do.