My usable screen size shrunk on Windows 8 after exiting Sims 3.

I have been playing Sims 3 for a while on my Windows 8 laptop without problems. However, this last time, upon exiting the game, my usuable screen size has shrunk to 2/3 of normal.  I cannot figure out how to change it, and I've tried rebooting several times.  I'm thinking that there's a Windows setting that the game uses that is supposed to reset upon leaving the game, but for some reason it did not reset.  I've tried pushing F11, but that just makes whatever window is open maximize to the largest size (which is the reduced size).  Since I can't attach a screenshot, the way my monitor looks is a smallish desktop with a wide black border around it.  I can't seem to make the desktop expand to fill the entire monitor.