Just a heads up, using Ambient Occlusion while playing games such as CoD4 is considered cheating.
What's your current graphics driver?
If we're running the same we could give ago at; me exporting my current settings and you loading them up.
Or, you could have ago at updating to the latest version (if you haven't) and select a "Clean Install" to reset your settings back to default.
Posted on Friday, 13th April 2012