Please provide more information about what kind of Hardware (your computer) and Software (the operating system [e.g. Windows 7]) you are using.
The first question set aside, have you installed the drivers for your graphics card (correctly)?
If not, please do so.
AMD (ATI):
AMD (ATI) Graphics Cards - Drivers - support.amd.com
NVIDIA:
NVIDIA Graphics Cards - Drivers - www.nvidia.com
If the drivers were installed correctly, are they up-to-date?
Reference:
[B]AMD (ATI) Latest Driver Version:[/B] AMD Catalyst 12.8
[B]NVIDIA Latest Driver Version:[/B] GEFORCE R304 Driver 306.23