I am running windows 7 64 bit with office 64 bit with 12 cores. I have a rather large Excel 2010 application that uses a great deal of cpu capacity. When my CPU capacity reaches 50%, my screens inside of the Excel windows go black and the system clock stops working. While this is happening I am only using 5GB of 25GB of available memory. I am not using a screen saver and I have the latest updates to my system including service pack 1. Even though the application continues to run during this blackout, the result is the same as being dead in the water. I can run my mouse over some of the icons in my tray and they come to life which makes me believe that the graphics card is at fault here. I am using two monitors, one connected with HDMI and the other with DVI. When I close Excel everything returns to normal. I occassionally get warnings from Norton that one of my cores has maxed out. When I view the CPU usage history, it appears that Microsoft is doing a good job of distributing the work across the cores. Well, I've blabbed enough here especially since I don't know anything about the subject matter. I would appreciate any things to try to prevent my Excel screens from going black. Thanks.