I think my Mac mini is possessed. Its certainly acting very strange. Im usually pretty good with computers but this one has me stumped. I have 3 hard drives with 10.10.2 on all of them. I have my main drive which I use everyday and I back it up everyday to my second drive with SuperDuper, and I also have a third drive that I keep around for basically emergency purposes. My most recent backup was yesterday. All of the hard drives are fairly new (a few months old) and are 4 TB. It all started when I booted from my main drive to my third (emergency) drive to look at an old document that was on there. When I was done reading it I went to Startup Disk and switched to my main drive again, and then went to the store. When I got back I turned my Mac back on, but received the circle with a line through it on my screen, so I tried to boot up again, but had the same results. When my main hard drive wouldnt boot I simply tried to boot into the backup drive. Surprisingly the same thing happened, it displayed the circle with a line through it. I thought that maybe the USB hub that both drives were plugged into went bad, so I plugged both drives directly into the Mac. That didnt help. I tried to boot into the third drive and that booted up fine. So I went to Disk Utility and did a repair on the first drive and the second drive. Both drives were OK. Tried to boot into the main drive again, this time I held down the shift key. Same results with the circle and a line through it. So I tried Command - R. Same results. So I held down the Option key and manually selected the main drive. Surprisingly it booted into the third drive. So I rebooted and held down the Option key again, this time I selected the backup drive. It booted into the third drive again. I tried to reset the parameter RAM (Option-Command-P-R) but it booted into the third drive again. Tried to start up in safe mode but again, it booted into the third drive. Getting frustrated I decided to do an Internet Recovery. It started to install Lion and when it was done downloading it rebooted - into the third drive. So I installed 10.10 and guess what? Yep, it rebooted back into the third drive again. I unplugged the third drive and booted up, and got the circle with a line through it. I plugged the third drive back in and it booted up to the third drive... It wont get out of this loop from Startup Disk and just keeps booting into the third drive, even though both the main drive and the backup drive report that they are OK. How do I get out of this loop? What else can I try to boot into the main drive?