The steam forums talk about some people having that wireframe problem a lot in Counter-Strike: Source. I don't know if a 100 percent solution was found or not. The first suggestion everyone has is always "The software is missing some files, delete it and reinstall it."

Which is a large pain if you downloaded the thing. And I'm not even sure if that fixes the problem or not.

Have a scrape round the steam forums and their FAQs and see if there is a definitive solution.
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Tony Fabris