Problem 6: No Sound, Sound Error or Audio Lag
Possible Solution 1: During game, game runs fine but there is no sound, Sound Error or Audio lagging, game is reducing the sound by a considerable percentage that you can’t hear it. The game may also be muting the sound on start, similar sort of problem was with Call of Duty World at War. Anyway, you can fix this issue by the following workarounds.

1.Start Game.
2.ALT + TAB
3.Go to your system try by your clock and locate the icon that looks like a speaker.
4.Now, Right Click on Speaker icon and chose “open volume mixer” or left click on it and click “mixer” underneath the volume slider.
5.You should now see Call of Duty: Black Ops volume control, drag it up to the top.

Problem 7: Freezes Fix
Possible Solution: You can faceoff this problem in Single Player and Multiplayer, if you experience a freeze while playing online; it is also possible that you may be having a network problem. If you are experiencing freezes while playing the game on console, try running the game from the disk and make sure your disk is scratch free or don’t have any physical damage.

If you are experiencing freezes on PC, make sure you have updated video card drivers. Disable any antivirus or firewall you have installed and see if that resolves the game freezing. If game doesn’t stop freezing randomly, you can try running the game windowed.

1.Go to Black Ops installation directory
2.Open the Players directory
3.Open the Config.cfg file in Notepad
4.Search for the line seta r_fullscreen “1
5.Change the 1 to 0
6.Re-run the game.