you should mention the type/version of your operating system and hardware. but very likely, it's a graphics driver issue... flicker-free animation/screen painting is one of the costlier operations of your computer (and something that's taken absolutely for granted!) and on some hardware, a vendor specific graphics driver may need to be installed... check out the support website of your computer manufacturer and try installing/upgrading the graphics driver... or it could be as trivial as what reddy said. or not...