iMac 2008 Core 2 Duo does not list my bootable USB stick in the boot menu? Hi i am trying to install OS X El Capitan on iMac 2008 model Core 2 Duo processor, and  4GB Ram. The way i followed is i created a USB bootable stick and insert to mac machine and restarted the Machine then i  pressed C key in keyboard and i waited more than 30 seconds then it is not showing any usb Bootable option and later it booted directly. Even i can`t able to Boot CD Drive also. can any one help me out here please.
Try:


Holding down Option at boot, not C. This will show every available boot option
Make sure you are using a USB keyboard attached directly to the machine