Things to try
Download the latest drivers for things like graphics and sound cards.
Install the latest version of DirectX
Lower graphic setings a little at a time and see if it helps.
If possible change the sound settings to something that might be a little less stressful on your system.
Ensure you have the v1.1 patch installed
All simple things that you have probably already trried, but still worth mentioning.
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Clan Leader and all around NICE GUY 