help please

hi everyone
just joined this forum, looks a great place to learn about motorcross.
i,m no mechanic so i hope someone may be able to help me out. i have a rm 250 1990 model and today i was riding my bike, completed a couple of laps on my local track,
thn i heard some unusal noises coming from the engine so i stopped the bike left it for a couple of mins then tried to start the bike again, i could,nt even kickstart the bike , the kickstart would,nt even move, so took the bike home, took off head and barrel and inside were the connecting rod is it was full of water and the connecting rod would,nt move.
could someone please explain to me what they think may of happened and what i,ll need to do to get my bike running again.
thanks for your hekp guys.

yes i drained all the coolant and engine oil, but i did notice a big piece of my water pump casing was broken on the inside, but i dont know if that would be anything to do with it.