I just picked up a "new"(gently used) Mid-2012 cMBP. It's currently running Yosemite(10.10.3). In any case, I tried to pair my Magic Mouse with it, and I couldn't get it to see the mouse. I know the mouse is fine, as I have zero issues pairing it with any other Mac. Just to test, though, I turned on Bluetooth on my iPhone(I normally keep it off) and couldn't see it either. I've tried cycling BT on and off as well as rebooting. The computer is still under Applecare so if the BT module is shot it's not a huge deal to have it fixed-I just dread a trip to the Apple Store(and time spent there that I don't have at the moment). Does anyone have any thoughts on other things I could try before a trip to the Genius Bar?