I have another thread about this but it's kind of buried so I started this because I'm desperate. That thread is here for background on my struggles; http://forums.macrumors.com/showthread.php?t=1844762 I installed a 120 gig SSD in my late 2012 mini. I did command r at startup and it went to the spinning World for an hour and ½ and then showed a screen with a big circle with a diagonal line thru it. All I could do was unplug the mini and plug it in again in about 30 seconds. Came up with both the HD and SSD showing and working!!! It was OK for several hours. All was well so I downloaded Yosemite to install in/on the SSD and when it was done downloading I got the message "SSD not properly ejected" and it is now no where to be found??? I restarted and still not there and it does not show in Disk Utility? I have not moved the mini, so it should not have popped off the connecter? Any thoughts?