Hello, I have a MacBook Pro 15 Inch Mid 2012 and suddenly began to experience a complete slowdown/no response from computer. No command possible and my screen gets stuck with a rainbow ball spinning until the computers battery either dies, or I hold on the power button to shut the computer down. The only significant change is the recent update of OS X Yosemite. Further Details: The computer at times reboots without a problem and for a few minutes (about 1 or 2) Im able to start a browser and navigate but then the rainbow ball pops up and thats the end of the computer responding. Ive been able to start up Activity Monitor but at first it shows no abnormalities that I can see and it fails to register anything once the computer stops responding. Any help would be greatly appreciated.