All my Source games have stopped working...

[daphatgrant]

I'm not sure what has happened but I played some No More Room In Hell last night and all was fine. Today I load it up, it starts and I get major artifacting and then it freezes with an audio clip loop. I've uninstalled and reinstalled it, I then tried checking Half Life 2's game chache and all was fine. I then tried Age of Chivalry and had the same artifacting, sound loop, and freezing. Lastly I tried Left 4 Dead 2 and again got the same results. In between the first 2 games I loaded up Crysis 2 and it played fine... wtf?