It's very hard to troubleshoot when you don't have anything to go on. The most common issues for Terraria are either faulty/misconfigured graphics drivers, or issues with .NET and/or XNA. Sometimes .NET issues can only be reliably fixed by reinstalling Windows. I hope we don't have to go there.
You could try updating/reinstalling your graphics drivers next. Sometimes weird things happens when they aren't ok. For performance reasons they aren't as fault tolerant as other drivers. If you are using a laptop, some higher end laptops have a dedicated GPU as well as a GPU for low power usage. Terraria used to have trouble with that before 1.4. Don't know how it is now. You should switch to the more powerful one before starting Terraria and not use automatic switching.
I wouldn't mind knowing a bit more about your computer, Windows version, CPU, amount of RAM.
Does other games work ok?