I'm unable to transfer files from my computer to my Lumia 520 and vice-versa. In fact, when I connect the USB, my mob is detected in "My Computer" as Windows Phone but I cannot access files; it appears to be empty while it is not. Glad if you could please help me. Thanks.
Have you removed any microSD memory card if present? This resource may offer some help: http://answers.microsoft.com/en-us/winphone/forum/