VLC doesn't have Blu-Ray playback capability out of the box. Perhaps previously you installed it but in the meantime you refreshed or Reinstalled windows or something?
In order to play Blu-Ray in VLC you have to have the AACS libraries installed. Now, this is where things get tricky, because as far as I can tell,
the website for it is currently down. That's a bit of a trouble spot!
I have it installed right now though and it largely involves two files; libaacs.dll for VLC itself, and KEYDB.CFG which contains encryption keys for playing
most commercial Blu-Ray discs. I've put those into a
zip file. I only have the 64-bit version of the dll though- so this only will work with the 64-bit VLC.
libaacs.dll goes into the VLC Folder itself. In my case it's under C:\Program Files\VideoLAN\VLC
KEYDB.CFG goes in C:\ProgramData\aacs
This doesn't give unfettered playback though. I've found a number of Blu-Rays, both movies and TV Show sets, simply don't work; This is because the encryption keys for those discs aren't in the database. I've also found a few that play fine but the menus for the disc don't work and I have to use "No Disc Menus" or it get's stuck.