First, go to Start > Control Panel > Hardware and Sound and open Device Manager. Expand the Universal Serial Bus controllers list, right-click on the driver and select Uninstall. After that, reboot your PC, connect the player to your PC and press Scan for hardware changes icon from Device Manager. Windows will automatically find and install the drivers. Also, try running the Fix It utility provided by Microsoft.
After that, download and install Sansa Updater, connect your device, launch the software and update the firmware.