HELP! My site went totally messed up!

After trying to play around with my General Settings and trying to figure out how to change the landing page to a different one, I thought I switched everything back to the way it was, but now I can’t even login! Logging in just brings me to the website and not my dashboard. Even worse, my website looks like it was hit by a train. Nothing is right…someone PLEASE help me out of this nightmare. I don’t even know where to start. This website is for my small business and I depend on it functioning. HELP!!