Good one Labob the website search. Over 80% are the Realtek Audio issues and in the control panel to hit "Sound" and hit the right device to work on.
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Thanks to Dollardogg, if you have Realtek Audio onboard, install this one (thanks again Dollardogg):
Click Link
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The last 2 weeks, I helped a few people by doing this:
1. Move or remove folder(s) of that server(what names in the Mods_Folder_Names, screenshot below). Or just move the "Mods" folder completely to your desktop or somewhere else to have a backup.
2. Use XI Downloader OR;
A) Start the game up, without entering the server. Go to "Options" and hit the button "Optimized System Settings".
Go out of the game and start Call Of Duty 4 MP again after 10seconds.
C) Once the game is started, hit the tilde key ` and
type above in the screen : /connect IP:port for example : /connect 208.100.42.50:28960
You have to redownload the server mod again and anything else as usual.
Give us feedbacks in return to solve this for more people if that worked for you. Good luck!