it comes up as soon as I press start though

When I log in, this comes up (I attached a file). I can log in but if I try to change server it comes up or if I log out and try to change account. I tried to go on the server I was originally on and it still doesn't work but it does work on a different computer in the house I live in, meaning that its not to do with the connection or the computer as it worked only a few days ago. Do you know what I should do?