I have a newer (well newer to me) imac, about 4-5 months old... I recently upgraded to yosemite... Ever since, when i shut down, the computer goes kinda dark but gives me a spinning wheel and wont "shut down" entirely unless i hard shut down the machine with the button. I have done a disk verification, nothing wrong, permissions verification, got those ok... even did that in depth diagnostics thing upon restart, that came back clean. I make sure all programs are turned off, all disks ejected (external disks and network)... no filevault thing, when it's working it works well, but it doesn't want to stop working. Any advice?