What is the problem with my Sears Garden Tractor?

I have a Lawn tractor that would not start when I pushed in the clutch/break pedal down and turned the key unless I got the clutch/break pedal in a certain spot. Then it would not start no matter what position the clutch/brake pedal is in. I thought it might be the starter switch so I installed a new one. When I push the clutch/break pedal down and turn the key it does not start. It does make a click noise when I turn the key. I can start by putting jumper cables on the battery and starter.