Hello, I received 2 older imac computers that both are running windows 7 (not bootcamp or dual boot) I would like to install OS X back on these machines. I have a bootable USB with OS X ready to install but I can't seem to understand how to actually do it. I have tried press and hold "c" while booting and got to a "grub". Everything I tried under "grub" did not seem to work (all from research, I have no coding experience at all.) like: root (hd1,0) etc' But nothing work, I kept getting this message: "kernel must be loaded before booting" Can anyone help me understand what would be the best and easiest way to install OS X back on these imac machines. Thanks for the help.