I recently bought a Husqvarna DRT900H, within 5 minutes of using it, the belt came off. I put the belt back on, made one round of the garden and the thing just quit and locked in place. I took the machine back to Lowes and they replaced it with a different machine, Now the belt on this one has come off, so I put it back on and adjusted the tension (per the owners manual) but the belt keeps coming off. What's the solution?