[Update: No kidding right after I posted this it locked up again. doh....] Computer Details: iMac 21.5" running OSX Mountain Lion Version 10.8.2 Processer is 2.5 GHz Intel Core i5 with 12 GB 1333 MHz DDR3 RAM I've had my iMac for nearly a year, all has been pretty smooth until recently when it has decided to start locking / freezing up on me (more details shortly). The only changes I have made to the system so far have been #1 I upgraded to 12 GB of aftermarket RAM from the stock 4 GB and #2 I upgraded to Mountain Lion when it became available. All of this took place pretty quickly after I bought the iMac so I don't feel that any of my changes have affected as I have been running the machine like this for nearly a year. What I did notice was there was an OS update about 6 weeks or more ago that was around the same time of my problem. Could have been a coincidence or not. When it locks up the screen just completely freezes, nothing responds at all, and often it gets stuck on the same sound. What I do notice though is that when I'm playing games especially more graphically intense, i.e. WoW (is the worst, will freeze up anywhere between 1 - 3 hours of gameplay) Minecraft (pretty stable for a long while, but still have had it lock up with this as well). Only once has it locked up while I was just in normal desktop non-gaming mode. Any help or advice would be wonderful, my 1 year warranty will be running out soon as I bought it on Black Friday of last year.