I have had some problems with sharing media from a Windows 7 machine to a Windows 8.1 machine. After some playing about I found that it was possible to re-ensure in the security tab in Windows 7 that ALL the folders that I want to share have the WMP security assigned. To do this, simply go to the upper most folder and ensure its present, if you need to, just un-tick the READ and re-tick and then press OK. It will then spider through ensuring that all sub-folders have it assigned.
Secondly, in Windows 8.1 make sure that your Windows LOCAL CREDENTIALS are correctly set up. To do this, go to the Control Panel, go to User settings. You will see an option to alter the Web Credentials and Windows Credentials. In Windows Credentials add the name of the PC that contains the music, add in your login ID and add in you password and press OK.
Restart Windows 8.1 and log back in. Then go to Media Player and head to the shared / streamed PC and you should now have access to all the music to stream through your local network…
Enjoy!