I have been working on some Mid-2012 MacBook Pros and I can't get one of them to boot into OS X no matter what I try. The laptop powers on to a gray screen with no chime and after about 30 seconds goes to a black terminal screen that says "No bootable device -- insert boot disk and press any key." I've tried bootable USBs which worked on other Macs, a hard drive that already has OS X installed, and even an install DVD to no avail. However, I put a Windows 10 install disc into the optical drive and it booted into the 10 installer with no problem. After some research it seems it may have something to do with BootCamp but that's as far as I got. Any suggestions? Thanks in advance!