If you’re using a hardware firewall within your router or suspect the issue might exist within your router, you should check your device documentation to clarify whether the router will accept or can be configured to accept media sharing connections.
Should you be attempting to share media with an Xbox, visit support.xbox.com for further information on connecting an Xbox 360 correctly to your network.
Attempts to share with MP3 or other mobile media players should work without a problem – however issues might concern your USB cable. A good way to check this is to try using a different USB cable, or try connecting your MP3 player to another PC or laptop.
Finally, depending on the nature of your media sharing issue, you might wish to test your network cabling/connection. A quick and easy way of doing this is by going to Start > Run and enter CMD to open the command line. With either the name or IP address of your router or another network device to hand Enter:
Ping 192.168.1.1 (or whatever your IP address or device name is)
The response from this should return several lines that display the same or similar speed values – but if any of these are listed as “Timed out” or with much lower figures, it is likely your network needs some reconfiguring.