multiplayer server connection issue

i have acer vista, and my multiplayer used to work fine then i had a friend download minecraft on a diff computer so he could play single player now my multiplayer doesnt work and i think its because he has the priority set to his computer or somthing. I can load the multiplayer maps but then what happens is it doesnt render they blocks and then completely lags out and disconnects me. It then says this "Java (tm) platform SE Binary is not responding"