The Steam overlay causes some older titles to experience glitchy behavior with graphics.
If you are experiencing some graphical distortion or you suspect your machine has been possessed by evil spirits, turning off your steam overlay may help to improve performance.
you can do this individually for specific games by going into your Steam's Library view and right-clicking on the game title then select Properties.
The option to un-check your overlay will display on the General tab.
After you’ve done this, close and restart steam, and then launch your game to see if behavior improves.
For further assistance with the Steam Client, we recommend contacting Valve’s support team HERE.