I am using a Samsung SGH-X520 mobile. I had purchased the same in second hand condition some weeks before. I had now arranged a data cable to back up my contacts in my PC. When I connect the phone to the PC it show up as a unrecognized USB device. I had restarted the system and then try it back again. If the message continuous then I will not able to install the phone to my pc. I am trying to do the same on a XP computer. Thanks.