Phone [Q] Lg optimus 4x does not detect pc + not registered

Hello ! I have a lg optimus 4x and i wanted to root it, but my pc does not detect it. I tried everything (its not in charge only mod) and i even brought it to repair shop, they could not do nothing. Do you guys know why it does not detect ? And also when i try to update it through the software update program, it tells me that its not registered. Do you know where to register it ? Thank you for your reply