Hi Guys, I've noticed over the past couple of weeks my main iMac has switched itself off overnight on its owna couple of times. Its odd because it's not scheduled to do this and the console logs just seem to stop without mention of problems. What else is odd is when press the power button after the random shut downs. The start up chime sounds, then, it goes straight to the lock screen that appears when coming out of screensaver NOT the initial mac login page. Its very unresponsive at first for a minute or two and there seems to be alot of disc activity. I've ran a full test with Tech Tool Deluxe and it hasn't found anything and am unsure what to do next. Any advice appreciated! Cheers EDIT: iMac is a 21.5" late 2009 model.