My 2011 Mac Mini (Core i7) has worked reliably for years, but just started refusing to boot from the internal HD. Appreciate thoughts on what I should do next, and whether this is a hardware or software problem (fearing the former, hoping the latter). Background: HD is a Crucial M4 SSD that I had an AASP install in late 2012 when I bought the gently-used Mini. OS is 10.8.5. I recently moved the Mini about 5 feet from its old spot in an attempt to run it as a headless media server, so turned on Screen Sharing/Remote Desktop and (initially) didn't have a keyboard or mouse attached. It is plugged into my TV via HDMI, and now has a keyboard/mouse connected too. Short story: Machine still boots from the recovery partition or external HDD, and can see & back up data on the internal OS X partition, but can't boot from it or the Bootcamp partition. Disk Utility and NVRAM resets haven't fixed the issue. Haven't tried an OS X reinstall yet. Details: #1. On pressing the power button, the gray-background boot screen and gray Apple logo come up. There also is the spinning round status indicator below the Apple logo, that just keeps spinning. I have to hard-power off the system by holding the power button. This started happening occasionally and now happens every time I start it up. #2. If I hold option, the boot volume selector screen comes up. I can see my OS X partition, as well as my Bootcamp partition (Win7) and Recovery OS X partition (and my backup FW 800 external HDD, if attached). But if I choose my internal main OS X partition, same gray nothing as #1, above. #2b. The Mini won't boot into Windows via Bootcamp, either. (Sometimes I get a flashing white C prompt-type cursor in the very upper-left corner of an all-black screen, and once the Win7 green loading bar appeared, but in no cases has it booted.) Not sure if this indicates a HD problem or if Bootcamp is tied into the OS X partition somehow. #3. If I boot from my backup HDD, I can see the internal OS X partition and all the files, and copy them to the external HDD. So, all the data (for now) appears intact. #4. If I boot from my Recovery partition or backup HDD, and try to select a startup volume, my OS X partition doesn't even show up, only my Bootcamp partition and external HDD. However, the first time I tried this, I could see my main OS X partition, but got the error message: "the bless tool was unable to set the current boot disk." #5. Disk Utility shows no problems when I verify the OS X partition. However, when I try to repair it, I get the error "Error: Couldn’t unmount disk." SMART status is Passed. #6. When I try to repair permissions on the OS X partition, I do get one out-of-the-ordinary error, presumably tied to turning on Screen Sharing/Apple Remote Desktop: "Warning: SUID file “System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS/ARDAgent” has been modified and will not be repaired." #7. As mentioned up top, I physically moved the Mini about 5 feet away to hook it into my TV and HD DVR. So, it's been physically moved before this problem started, but not at all jostled. I also opened the bottom hatch to blow out any dust bunnies. RAM is properly seated and registers OK when booted. #8. I tried resetting the NVRAM, and got the appropriate double-chime/restart feedback, but no effect. What Haven't I Tried: I haven't yet done an Archive and Install or fresh install. Appreciate your thoughts on next moves. I'm guessing a system reinstall might be the next step? Anything else I can do short of that to "bless" the HD (or the OS X equivalent?) The fact that the machine boots, shows the OS X volume, and lets me pull files off it makes me hope this is not a hardware problem. Could turning on ARD/Screen Sharing be causing an issue? (I can't imagine how but who knows given the Disk Utility results). Thanks.