If video card built by AMD/ATI,

If so, the Vari-Bright feature must be on. To fix this go to:

1. AMD Vision Engine Control Center (or AMD Catalyst Control Center)

2. Power

3. PowerPlay

4. Uncheck the “Enable Vari-Bright” option.

download the AMD Catalyst Control Center (AMD Vision Engine Control Center on other laptop) at the AMD/ATI website
here:

hxxp://support.amd.com/us/gpudownload/Pages/index.​aspx

and that will fix your problem.