Bolens Lawn Tractor Will Not Start?

I have a Bolens 13.5 HP lawn tractor with B&S engine. When trying to start it, all I am getting is a clicking sound; similar to a car with a low battery. I have charged the battery to a full 12 volts, but no luck, still clicking. The tractor is only 3 years old. Any suggestions for what I can do? Thanks.