iPhone not recognized by PC but only mine

Apparently my laptop computer is not recognizing my iPhone in anyway. I've tried all the troubleshotting tutorials on Apple's website to fix it but I wasn't able. I've cleaned my Windows 8 operative system completely (refresh, all programs gone) and reinstalled iTunes, the iphone doesn't get recognized... occasionally it pops on itunes grayed out for a second or two but dissappears soon after. Than I've installed a fresh copy of Windows 7 and put iTunes on it. The same thing happens!! But than when I try to plug it on a friend computer everything works perfectly, iTunes detects it and syncs... I really can't understand what is this problem neither how to fix it. Can you help me? Thank you very much for reading, I'll be waiting for an answer!