OK, I've been Googling and searching various Mac forums for a few days intermittently now, but can't find a close enough case that matches mine so here we go: My mid-2009 MBP, in the last week, has stopped responding to the power button while the computer is powered on. If I try to shut down or restart via the menu, nothing happens. Nothing suspicious is showing up on the Activity Monitor under All Processes and no applications are opening. I was changing some things in the System Preferences pane, but I haven't a clue what I could have possibly altered that would cause this. The only ways I can shut down right now is by doing a force shut down by holding the power key down (so I'm guessing that switch isn't broken) or by opening up Terminal and entering: sudo shutdown -h now. It's worth noting that I've run MacKeeper, OnyX, repaired the disk/permissions via the RecoveryHD, and I just did a clean install of the OS within the last month. Thank you. I can see that this forum is very helpful and I will greatly appreciate any help!