Board Thread:Help Desk/@comment-24092835-20131027141208/@comment-5604521-20131031014500

Do you have it through Steam? If so, try Verifying the Integrity of Game Cache for Terraria and when that's finished, see if it works. Try it and tell me if it doesn't.

http://www.ehow.com/how_8431414_verify-cache-steam.html

Also, I am assuming you're using Windows? 7 or 8?