I have a Craftsman LT 2000 model lawn tractor. The belt broke the other day, so I replaced it. I thought I got it all back together properly, but now... The blades wont turn if I have the blade height set to #1 or #2. If I have the blade height set to #3, the blade turns but kills when I try to cut. If I have the blade height set to #4 or #5, it takes longer for the blade to engage but it does cut ok. What could be wrong?