Try to make create a shortcut to iw3mp.exe and put it on your desktop. Start the game with that instead of through Steam steam and see if that helps. Installing COD4X as @LilAcorn suggested can solve alot of problems. The only problem that I've experienced with running COD4X is with hearing gun shots and RC Cars in maps that have background Ambient sounds such as explosions,Birds,Frogs ect ect. Pretty annoying but alot better than randomly crashing.
Download cod4X here. Extract it to your game folder. Open the cod4x folder that it created and click on Install to run the installer. Close your game folder and run cod4. https://cod4x.ovh/uploads/short-url/d5Tcz0e3rFBEE20Sw5Ep9wi0RqR.zip
If you are using a USB Microphone, plug it into the back of your PC. The front ports usually have a lower Hardware Priority.
Just an Example: Alot of motherboards will not allow you to Flash the Motherboard Bios from the front USB ports because of possible file corruption caused by the lower Hardware Priority. It can also cause a USB Mic and USB Headphones to randomly disconnect.