Diablo 2 critical error!!!

[:1]ok guys, i just got diablo 2, last time i played it was back in 2002 anyway i installed it on win 7, and when i run diablo 2 it takes a while to start like 1 minute, and when it does everything is negative in color (pink and green) until i click the mouse and even then while playing the game it has a color problem but just the slightest. also my connection keeps getting interrupted, like im playing a game, the amount of people don't matter but an hour or so in it starts to lag like if i try to go through tp it wont let me and if i pick up gold it wont let me then it says connection interrupted and i get kicked. it happens very often and i want to know how to fix it, the last time it happened it said something about another person using the game and it showed my name. also after i close diablo 2 it says critical error, only 1 copy of diablo 2 may run at once, it been saying that ever since i installed it, guys what should i do.|||i haven't win7 ... try to use administrator account