Originally posted by Canada_Rockies Good luck with that. Sometimes it is just a software glitch, but other times with a 7 year old computer, it could be a component failure, and it isn't worth the hassle of replacing it in an older machine.
Apple have made it progressively harder for anyone to fix their computers, especially the iMacs. I can upgrade the RAM and drives of an iMac G4 with a Philips and a Torx screwdriver, no other tools needed. I wouldn't even try to upgrade a G5 or one of the Intel models because it's almost impossible to get to the drives without destroying the screen or damaging the motherboard.
Re the non-booting iMac - if it's one of the models that still has slot-in memory that you can access from outside the casing (I think that one would be) it might be worthwhile pulling it, vacuuming the slots, and putting it back. That's about the only possibility you can check without serious technical skills.