Terminal wiped all files. With rm -rf /!

Due to studio circumstances I have acquired an imac that has been wiped with the dreaded command in terminal. I have a bootable USB with the operating system install disk partitioned and ready to go. There are no original application left on the computer including disk utility. So the issue is that when I get he prompt to restart the computer to start the installation process, the restart chime happens and then the computer restarts as usual without acknowledging any previous command to start the installer. Please help!