I would first try force closing steam with task manager then trying to start it again, if not then go ahead and try to make a log file and send it here.
creating a log: simply go to your steam library, open Terraria's properties, and open Launch options, paste "-logerrors -logfile '' into the box. The next time you launch, it should make a log in Documents>My Games>Terraria>Logs.
Dunno if this will notify you so I'll reply here for you to read above, I was gone for a day or two haha!You can try deleting the config.json file in your terraria folder: Documents\My Games\Terraria
Never ended up finding out how to do this and my game is still broken, I have uninstalled and reinstalled the game and steam itself. Zero clue why it won't work, super frustrating to sit and have zero way to contact anyone knowledgeable besides on forums of good people such as yourselves.You can try deleting the config.json file in your terraria folder: Documents\My Games\Terraria