Many Windows Vista and 7 users got problems with the brightness setting. If you set r_gamma to values higher than 1.0, or move the brightness controller to the right it just stops or the screen gets even darker.
Follow these steps:
1. Right-click CODMP.exe
2. Click Properties
3. Open “Compatibility” tab
4. Check “Run this program in compatibility mode for”
5. Click the box and select “Windows XP (Service Pack 3)”
*Note – If using Windows 7, also check the “Run as administrator box”
6. Press OK
A few more ways to try and fix brightness issues!
If your monitor turns darker in fullscreen and the game doesn’t respond to brightness settings, you can fix it with setting r_overBrightBits from 1 to 0.
If your monitor turns very bright when attempting to Alt+Tab ↹ out of the game, you can fix it with setting r_ignorehwgamma from 0 to 1.