Car makes buzzing sound when about to start

I just replaced my water pump, and put everything back together. The car wouldn't start but would turn over. the timing belt had torn teeth. Replaced it, made sure the timing was correctly aligned, using autozone.com's site. So, I thought it would work now, but now all the belts move but won't turn over. When I turn the key it makes a buzzing sound near the starter, and won't turn over. I don't know why it's doing this. It didn't do this before I replaced the water pump. I think someone that was with me may have tampered with it. What's causing this not to start? Thanks.