Nokia Lumia 520 - Why can't my computer recognise my Lumia 520, 521, 525 or 526 phone after I have connected them by USB cable?

Check your computer's operating system.

If the operating system is Window XP, for example, the latest Microsoft Windows XP Service Pack 3 and the latest Microsoft Windows Media Player 11 must be installed.

Reboot your computer after unstalling Windows Media Player and try again.