You don't need to reinstall TF2 just yet. Right-click it in your Games list, go to Properties, Local files, Verify integrity of game cache. This'll check the game's encrypted files for corruption.
If you do end up reinstalling, it'd probably be better to just delete the "\SteamApps\USERNAME\tf2\tf\materials" folder rather than the root folder or the GCF files. At least at first, to see if it works.