So a few months ago I fired up my iMac and a bunch of computer gibberish appeared in bands on the top of the screen. I rebooted and it just didn't start up. Fans were on but nothing else. Anyway, went on vacation, came back and today decided to see whats up. Fired it up and got the familiar chime and Apple logo pops up. ALL IS FINE! YAY!.... or not, then this comes up. I turned it off, then tried to fire it back up and fans spin but nothing happens. ?