Edit: Please ingore, I forgot that the play can only use DLNA and not network shares. Luckily a good friend of the forum noticed before I spread too much dissinformation. :flushed:
You are connecting from you WD PLAY to a shared folder on your windows7 computer. The WD can only see files that are inside the shared folder. You need to figure need to either figure out which folder on the PC is shared and add your videos to it, or share another folder that already has the video files in it.
You can see what folders you are sharing in Windows7 by:
Right-click Computer > Manage > Expand Shared Folders in the left pane > Shares will show all folders that are being shared.
The ones with $ in front of them won’t be seen by your PLAY. They are generally for the system to use.