Javier,
Does the pen you purchased look like the old pen you had? What model board do you have? Is the pen grey with an orange band or is it solid grey? There is a knowledge base article that may help. Please visit www.prometheankb.com, select your region/language, in the search box type in 10411, the title of the article is - ActivPen- Do all Promethean Pens work on all Promethean Boards? (case# 239884)
Thanks!