I purchased my tractor 4 months ago. Today as I was mowing my yard, when I wanted to stop, the brake would not engage and the tractor kept moving. When I tried to re-start the tractor, although the tractor was in park, the tractor began to move again. Any suggestion as to the cause or diagnosis to this problem?

Does it still have a warranty? Otherwise, what kind of trans does it have, manual transaxle ( clutch to change gears ) shift on the go, hydro? If it's a transaxle, get under it, there will be a rod, from the clutch, ( really depends on what the mower is ) to the transmission, there will be a round metal disk, that's the brake rotor, make sure the rod hasn't popped off, or the back nut hasn't walked off what actuates the brake pad. Use red thread locker on it if its loose and tighten it up.