If you're moving the brightness slider in options without having any effect on the game (and game is still very dark), here's the solution that worked for me:

1. Find Call Of Dity config file. It's located in <path-to-game>\Main\config.cfg, for example, c:\games\Steam\SteamApps\common\Call of Duty\Main\config.cfg
   
2. Find the following line: seta r_overBrightBits "1" and change it to the following: seta r_overBrightBits "0"
   
3. Find the following line: seta r_ignorehwgamma "0" and change it to the following: seta r_ignorehwgamma "1"
   
4. Play the game, it will be brighter (at least the night levels will be playable).

The position of the brightness slider doesn't seem to have any effect, though.

If you have an ultra widescreen monitor, you might have an issue with game interface being off-center, and some controls not visible / accessible, because they're out of screen bounds. This happens if you have modified the default interface scale in Windows (so it might be applicable to non-UWQHD monitors with modified UI scale, I simply don't have a way to verify this).

How to fix:

1. Find CoDSP.exe, right-click it, and click on Properties:
   
   
2. Go to Compatibility tab and click Change high DPI settings:
   
   
3. Click the Override high DPI scaling behavior checkbox and select Application, then hit OK.
   
   
4. Click OK to close the dialog.