I have been booting my 2011 27 inch imac from an external lacie ssd for about 5 months now with no problems. But now my imac will no longer boot from it. The only thing I did was shut down the imac and when I went to start up again I just keep getting the spinning wheel. I hardly ever turn my imac off, I usually just put it to sleep. But we had a bad storm, so I figured I'd turn it off because one time the electricity went off while it was asleep and when I went to turn it on, this same thing happened. I was able to get it to boot up from the ssd again by booting from the internal hdd and then I unmounted the ssd and remounted it and then I could boot from it again. I tried that this time and it would not work. I tried to boot my husband's macbook pro from it and it does the same thing the imac does, just keeps the spinning wheel. It will spin for a few seconds, go away, the screen will get a little brighter, then the spinning wheel comes back, over and over. If anyone has experienced this before or knows what to do, please help. I did verify and repair permissions and verified disc, but it said it was ok. Thanks Oh, I'm running version 10.8 if you want to know.