Having a MASSIVE problem with my cassette, need advice.

So I ride my bike (2012-13 Schwinn midmoor) to and from class and work every day, never more than about 5 miles a day. This morning, before I started my ride to class, I noticed that the cassette isn't catching on the wheel at all. It was fine last night, there were no problems. But as of this morning, moving the pedals has zero effect on the wheels. Backpedaling doesn't even make the normal clicking noise.

Do any of you have an idea of what the problem could be? It's been fairly wet and occasionally freezing lately, if that helps. I'm hoping I don't have to replace any of it right now