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