Go to C:\Program Files (x86)\Steam\steamapps\common\titan quest\Videos (or wherever you have Steam installed). Look for the following files:
TQCinematic.bik TQGameIntro.bik TQLegal.bik TQLogos.bik
Rename these files to something else, like [oldname].original. Right-click in the folder and chose New -> Text Document. Do this 3 more times, then rename the new text files to the names listed above.