I have an iMac 27" in for repair here is the problem: the hard drive is bad, it was booting from HDD now it won't boot at all. I've tried unplugging hard drive and booting from usb and cd. I've tried every boot combination possible. Holding all will only display hard drive, if hard drive is unplugged it it will bring up a grey screen with cursor. I can boot into single user mode but will not do much because the HDD is bad. The only boot options that do anything are: netboot, PRAM reset, etc. Holding C will not boot, option will only bring up hard drive if it's plugged in as stated earlier. This problem really has me stumped, maybe someone can shed some light. Thanks in advance.