Yesterday got a secondhand core duo imac and was transferring data from a backup and I interrupted it . Now imac will not start, get the above message. Writing on the screen starts " devfs_kernal_mount: failed to find directory "/dev"" and more. Panel says you "you need to restart computer. Tried holding various keys on startup including cmd., option, P & R but no good. Snow leo[pard is stuck in drive.Help.