So I'm browsing the web, listening to a podcast when the track starts to skip, and all of a sudden a dark transparent sheet starts filling up my screen from top to bottom. At first I thought it was going to be one of those annoying pop up ads, but then I got an alert that said: "You need to restart your computer. Hold down the Power button until it turns off, then press the power button again." I did so and everything SEEMS fine... This is the refreshed 2010 Imac so I'm really concerned. Anyone have any clue?