thats aero peek, it looks like it not functioning correctly, it should show the thumbnail of the open window.
to check you could type services in the start menu search box.
click the result with the cog, and in the services window scroll down to desktop window manager session manager,
click on it to highlight it then in the left pane click start this service, if it is already running then click stop this service then click start this service.
you should then see aero peek as it is intended,
then decide if you want to disable it.
try it with several windows open to get a better idea.
if you decide you want to turn off aero peek then here is a tutorial how to from brink Aero Peek - Turn On or Off