If your PC still won't see the phone, you can force a driver refresh: Open on your PC. Find Portable Devices or Universal Serial Bus devices . Right-click on (or "Unknown Device") and select Uninstall device .
Are you trying to or are you looking to flash new firmware onto the device? RM 914/lumia 520 driver - Microsoft Q&A skachat draiver dlia lumia 520
The Windows Device Recovery Tool is the official software designed to fix phone issues by reinstalling the correct firmware and drivers. If your PC still won't see the phone,