In order to fix the problem, right-click My Computer/Computer icon, select Manage and open Device Manager. Expand the Universal Serial Bus controllers list, right-click on the driver and press Uninstall. Reboot the PC, connect the phone through the USB cable, press Scan for hardware changes icon from Device Manager and reinstall the drivers.
If the PC is still not recognizing the device, try running the Fix It utility provided by Microsoft. It is specially designed to fix all major USB related problems. After that, you can sync the phone with the computer using the latest version of Samsung PC Studio or Samsung Kies.