Windows XP activation causing problems

hello everyone,
about a month ago, i installed windows xp proffesional on a brand new machine, i activated my copy on the internet and it was deployed at a school. a week ago, one of the users said that it was asking that the OS be activated but when they would try, it would say that the copy of windows has already been activated. it now logs them out when they try to log in. is there a way that i can solve this without having to contact microsoft