Hardware: Macbook Pro Early 2011, upgraded to Corsair 16gb ram, data doubler instead of optical drive currently with the stock 500gb hard drive. SanDisk Extreme 120gb SSD in the main hard drive slot. Software: OSX Mountain Lion I was running this setup fine for about 7 months when all of a sudden my computer freezes up and I have to power it off manually. Upon restart, the computer showed a circle with a slash through it (I have found online that this is a boot efi issue). So I decided to take my SSD out, read it in an enclosure through USB and it read fine on other computers. To make sure though, I wiped the drive clean and got ready to reinstall OSX on it. Turns out the computer freezes up when reading the drive in Disk Utility (through either USB recovery or internet recovery). Again the drive reads fine in an enclosure. And surprisingly the drive even reads fine in a different Macbook Pro (2011 version as well). Right now I have an install of OSX running on my backup hard drive, the one in the optical drive so that I can use my computer. Putting my SSD in causes the computer to freeze up at login screen. What is going on? The SSD seems to be fine. Putting a different hard drive in the primary SATA slot works fine. Just this particular drive causes lots of weird problems. Any suggestions, similar issues, thoughts on fixes? Any help is greatly appreciated!