Ltz prombles!!!! help!!!! fast!!!!!!!!!!

Hi, i just traded a guy my 98 kx250 for a 2003 Ltz400. The problem was that it need some work, My friend his dad and i took off the side plastics and the gas tank, we took out the spark plug and it was full with water. So i was riding it and it was fine. i was pulling out a lil later that day, and my sproecket bolts came out, and the chain DID NOT break, but it got jammed up near the shifter and was hard to get out. after that it would not turn over, only would click, then we tryed to pop start it and it started to turn over again, so idk wat the problem is. I need help!

sounds like exactly happend to mine some teeth off the reverse dog gear got cause in the tranny gears and wouldnt budge an inch...lucky it didnt break the case

So wat do i Have to do?