iMac Intel bought Nov. 2007. Last week I tried to install a Seagate 2T external HD, and after following their tech support instructions for formatting it for Mac, my iMac went berserk (disc wouldn't eject, trouble booting up, wouldn't recognize Disk Warrior). I took it to Genius Bar. They ejected disk by holding down mouse button while powering up, exactly the same thing I had done, and for them it worked. They ran diagnostics and found one problem with the HD so kept it, erased HD and reloaded Snow Leopard. Got it home, followed Migration instructions to reload stuff they had erased, and a bunch of it didn't show up, so I went to a Time Machine back-up and copied it. It might have been the back-up from the date I tried to install the Seagate external. IMac went berserk again, won't cough up my Disk Warrior disk (doesn't even seem to recognize that there is a disk in the slot), won't power up correctly, stuff still missing. We tried leaving it off overnight, depressing power button for 20 seconds, then booting up holding down mouse button. The only odd thing that happened was that in one power-up attempt a bunch of gray and beige dust flew out of the rear blowhole and caused the fan to whir endlessly until we powered down again. My questions are, in no particular order: 1. If my iMac has a Seagate brand internal HD, is it possible that in trying to reformat the Seagate external by erasing it I damaged my internal HD? I can't check because the Profile function is one of the things that isn't working. 2. Is there something that I could have contracted from the back-up disk (malware, virus, poltergeist) that would cause my internal HD to mutiny? 3. Could dust build-up be causing all my problems? I clean it as best I can, but with these iMacs there's no way to blow out any dust that gets inside. 4. If this were your computer, given its age (our Apple Care expired two months ago), would you opt for repair by Apple, repair by someone who comes to the house so they could trouble-shoot everything (cords, keyboard, mouse, etc.), or would you call it quits and start shopping for a replacement?