Once a while, and i'm not sure what the trigger is, when i try to open a window of a program (in this case steam.exe) via the taskbar the taskbar and screen flashes. The best way to explain is that it looks similar to when explorer.exe restarts. It happens quite often. Sorry i cant provide anything too specific, but it happens quite frequently when i try to open a new friend chat when i see it in the taskbar. 

Screen flashes can occur when the display resolution or color depth are modified. Make sure the desktop is already in a mode preferred by the app (usually true-color).

Power events can also cause a flash. Check Monitor Properties (under Display Properties -> Settings -> Advanced -> Monitor or similar) and uncheck "Reset display on suspend/resume."

The OP is just experiencing known stability issues with Aero Glass that cause compositor to crash and its recovery causes the screen to flash. It's already been brought up in other topics.