Replying to Crazy internet

So I have this laptop I borrowed from a friend, and there is a small problem. I have tried as much as my computer knowledge allowed me to. What happens and happened is that there are 3 users. Now there is an interent connection, and at first it worked under my user name and another, and then now it no longer works under mine either and only the last user name. However, it appears to know it is there, because certain things like auto updates will still work, just not MSN or Explorer etc. Anybody have any idea. Help would really really be appreciated. Also, sorry if this is suppose to be in another thread category. Thanks!!!