Tank you for the answer.
Indeed, i think the problem is from there. But how can i get this last driver for Windows 7? http://downloadcenter.intel.com/SearchResult.aspx?lang=eng&ProductFamily=Wireless+Networking&ProductLine=Intel%C2%AE+Centrino%C2%AE+Wi-Fi+Products&ProductProduct=Intel%C2%AE+Centrino%C2%AE+Ultimate-N+6300&ProdId=3408&LineId=1784&FamilyId=1783
They published that for windows 8, and it didn't work on my windows 7 computer... :/