Why won't my car start?

I've been having trouble with my car lately. Yesterday morning, I went to turn on my car and...nothing! It was complete silence...no whirring or clunking or whooshing. However, the lights in the car and the radio still all work. I know for a fact that it can't be gas related because I have 3/4 of a tank. What could be causing this? We're baffled and would like to get a few ideas before pouring a bunch of money into this.