Please help with my cod4 problem

Here's a few things you could try:

Close all background programs such as Antivirus and FRAPRS, etc.
Try again.

1-Resinstall your Videocard drivers with the latest version available and install the latest COD4 Patch.
2-Try the game

3-Resintall the game
4-Try the game

5-Perform a ScanDisk
6-Perform a VirusScan/Spyware Scan/etc.

7-Try and disable your RealTek Network card (or other devices that might be causing this).

8-Reinstall your Videocard drivers but perform a CleanDriver Registry before you reinstall them.

***If buy now, if you have the same problem, it might be hardware related***

Then I would have to know if you problem only occurs with COD4 or with other games as well.

I'll assume you have a legit copy of COD4.

Disabling your network card.

Option A: Bottom right of windows screen where you have your mini-icon (Time and Date). You can right click and disable the device from there.

Option B: If option A fails then you can go in your Control Panel - Systems - Device manager - and disable from there.

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Further troubleshooting would be

-Disable and Unplug your Wireless device (if that's what you have).
-Uninstall your network card drivers and take out the card before your next boot.