I've created a login form and other pages that keeps informations about the login.
All works fine on my pc and other my devices, but my friend with windows XP is unable to keep sessions from a page to another, either with firefox and chrome, while from his tablet all works fine
I'm assured that firefox is setted to keep cookies from alla sites, same in Control Panel -> Privacy of windows XP

I don't know what else i can do!
My site have a tk extension, maybe it's part of the problem?