Windows 7: Counter Strike Source textures glitching?

Hi, I today I decided to play some CSS with my friend, I haven't played it in a while and now whenever I try and play, it shortly just glitches and looks like this



Please help as I love this game to bits.

First thing you should try is verifying the game files. In steam, right click the game in your library and choose: properties > local files (tab) > verify integrity of game cache. This will scan each of the game files to see if they are corrupted or missing, and anything broken will be redownloaded. If you still have problems after this, you should try a full reinstall.