My iMac will not boot past the grey screen. No Apple or spinning gear but I get a startup chime. The machine will intermittently reboot and chime but it still remains stuck at the gray screen. This happened the other day and I just left it and came back a couple of hours later and my desktop was up, I just thought it was a glitch. I have tried booting to the CD by holding C on power-up and have reset the PMU and PRam but no dice. Can someone out there help me? Please!