Windows Media Player is not capable of playing Blu ray structure as far as I am aware. I just tried it with the latest version of WMP and it says the disk is empty when I inserted a commercially made blu ray disk, and did the same when I mounted an ISO in VirtualClone Drive.
To playback blu ray on the computer you will need one of the software packages meant for this, like WinDVD, PowerDVD or Arcsoft Total Media Theater.
You can use one of the free programs like VLC or Media Player Classic HomeCinema to open the largest m2ts file found in the Streams folder. This should start the main movie on most blu ray video, but playback may not be as smooth as with a commercial program. Blu ray movies made with seamless branching might prove to be a challenge for those free players.