Xbox 360 Media Sharing With Windows 8← Back
The first thing to check is that under Stream -> "More streaming options", you have allowed your Xbox 360 to stream media. If that hasn't been enabled you're destined for the fail whale.
In Media Player, you will also need to right-click Videos (or Music) and add your media locations to the list so that WMP indexes them. If you have lots of media files in the new location, WMP will take a while to index it all but you'll gradually see it appear in the respective library within WMP. If you check the security permissions on your media folder at this point, you'll find Home Users has been granted Read permission to all files and folders.
On the Xbox, I exited back to the Home screen then drilled back down through the video options and was able to view my TV shows and movies.