I had to make a bootable CD to use in order to access a secure website using a cac card reader. OSX does not support Active Client middleware like windows based systems do. Sure would be nice if they would fix this.
I had the same problem on a 17 imac one of the original Intel machines. We had switched the keyboard to one of the new ones. So in order to get the boot to recognize that the "c" was be held down we need to switch back to the original keyboard. Then all worked fine