I have a mid-2007 iMac that will not longer boot... Yesterday it rebooted itself and I couldn't figure out why... fast forward to this morning.. i woke up to the chime noise. the screen remains black and it seems to cycle the attempted boot process halfway through the chime noise (at this time you hear the HD start to spin up about half a chime and it reboots itself).. I've tried all of the option+% commands and holding down d,c,etc. with no luck. Holding down the power button for a while will make a loud beep. I'm wondering if this has to do with the aftermarket ram i installed over a week ago. i tried putting in the factory ram and resetting the ram to no avail. Could the firmware be corrupted? If so, can someone point me to the correct firmware to download for a mid-2007 24" imac?