Steam will examine the game’s files and – if any problems are detected – will re-download the corrupted files from Steam’s servers.
To validate a game’s cache, right-click the game in your Steam library and select Properties.
However, this may not always solve the problem – if the problem has already started occurring, the gameplay may be glitchy until you relaunch the game.
The easiest way to do this is by launching a game, alt-tabbing out, opening the task manager, right-clicking the game’s process on the Processes tab and using the Set Affinity option.
Steam is generally pretty stable, but every now and then you’ll run into a problem.
This guide gives solutions to common problems you’ll encounter in Steam, from games crashing or not working properly to Steam failing to launch.
Instructions on how to get these can be found right here.
Also, remember to include any error messages you get (screenshots are very helpful) as well as what you were doing in the game when it happened.