Sorry I don't get the point. Did you buy it from us? If so the simcard is already active. If you bought it in Italy at a shop it should active as well. If you bought it from someone else I cannot help you. Wind prepaid cards are preactivated, from the moment Wind receives your documents (passport, CF) they enable it to make and receive calls, there's nothing you have to do on your own.
To activate the Mega NoLimit just send an SMS to 4533 writing MEGA SI.
There's a topic about Wind data offers
HERE.