fedora 15 with gnome3 often flash screen on ati HD2600 graphic card.
 

My hardware is HD2600 , and OS is fedora 15. The desktop is gnome3. When I drag mouse to left top of the screen ,the screen flashs. After running OS for about 1 hours or later, things go terrible, all the icons are not shown normally .
What's wrong ?

Could it be that the corner is something like an "active spot" (hot spot?). In KDE one can usually switch those off in the KDE-menu but I have no Gnome3 (yet).