A window pops up and says "Origin Already Running"... what do I do?

So I have bought myself Sims 3 about a month ago and it has been working perfectly until today. This morning, the game launcher wouldn't even open. So, I tried turning off the computer, and came back to it a little later. I tried again a little while ago and a window pops up saying

"ORIGIN ALREADY RUNNING: Only one instance of Origin can run at a time. Please check other Windows accounts to see if Origin is running."

So I checked the other Windows accounts, but it wasn't running. It wouldn't make sense if someone hacked into my account since it worked perfectly yesterday. Plus, my password is somewhat difficult to guess, and most people don't know that I have this game. 

Please help! Sims 3 is my all-time favorite game and I spent most of my allowance on this game. Help!