If you want to launch tf2 your computer says that steam found a problem with your local game file and that game files will be re acquired from the steam servers what can you do to play again

It sounds like something is wrong with your actual game files, this might happen if you modify the game or if you downloaded some custom sounds and stuff from servers you connect to (maps, sounds, models etc.) Try right clicking the game and clicking properties, local content and clicking verify integrity of game files. You can also defragment the cache by clicking 2 buttons below that. Hope this helps ;)