Why wont my 99 audi's starter turn over the engine?

I have a 99 audi and it seems fine and everything is all kept up. It's a 99 audi A6 quattro with 124,000 miles on it. It was just running yesterday and now today the starter wont turn over the engine. What could be the problem?Why wont my 99 audi's starter turn over the engine?Sounds like the neutral start switch has failed. I am guessing this is an automatic. Or, the cables going to the starter may be loose.