Apple have recently announced a recall program for all iMacs with internal 1TB Seagate Hard Drives. These hard drives fail unexpectedly with no prior warning. We noted the failure of these hard drives in a post back in 2009.
You can check whether your iMac has an internal 1TB Seagate Hard Drive by entering your iMac Serial Number at this link.
This recall program has now ended. If you have one of these hard drives that has failed you may be interested in our Mac Data Recovery Services.