Ford Wind star 1998 wont start?

I have a 1998 Ford windstar, it worked fine yesterday and now its not working at all. It wont turn over. It will click once when i try starting it and the lights go on and that's it. Is this a alternator? Almost everything in this had been replaced, only things that haven't been replaced are the engine, tranny, and a few other things. I don't know what to do. Does anyone know what it is? Or even have a similar problem?