Problem about John Deere Riding Lawn Mower.?

I have some problem about John Deere Riding Lawn Mower. I’m an international student, so maybe I can’t describe well but I try to say clearly about my problems. I'm now having a part-time job which is cutting lawn in my college and my boss went to vacation this week. Unfortunately, once my boss left, I got some trouble today. At the beginning, the mower could run but it didn’t cut grass. So I thought maybe the belt was loose and I checked it and replaced a little bit, then it worked well. However, in the afternoon, by my careless, I touched some metals on the ground (I don’t know what it is), then I heard some a loud noisy under the lawn and I was scarred at first. And it seems like the two blades conflicted each other. I don’t know why they will meet each other. After a while, I restarted the mower, it didn’t cut grass again. Then I checked again, it seems that only the left blade works and the right doesn’t work. So I lay down and tried to twirl the right blade. Then I restarted mower again, the two blades conflicted and made a very loud noisy again. I don’t know what’s the problem could anyone help me? Thank you so much!