Downloaded it, played it, and everything worked… but I tried to start it again through steam after restarting it and there was no way to launch it!
Same problem here…
Put Black Mesa Folder in Steam/Steamapps/Sourcemods. Restart Steam and you will find Black Mesa in your library!!
If you used the setup.exe (self extractor) it SHOULD have put it in you Sourcemods folder. As Trojan stated, if not them move it there and restart Steam. It will not show in your library until after you restart Steam.
It’s already in that folder, and I’ve restarted steam three times.
I had same problem, I placed my folder in Sourcemods, and after that I saw Black Mesa in my library, dont know whats with you then, sorry…
So your path looks like this?
Steam/Steamapps/Sourcemods/BMS
If so, then I’m not sure what could be the issue. You could try re-installing of you haven’t already.
Steam looks for a gameinfo.txt file in Steam/steamapps/sourcemods/modnamehere/gameinfo.txt. That’s what it uses to add it to the steam list of games. Also for the record, the Black Mesa folder needs to be named ‘bms’.
If Steam isn’t detecting it at all, that may actually be an issue with Steam, rather than the game. Just having a properly-formatted gameinfo.txt in that folder should cause something to be listed.
My folder name is not bms, but thank god all works fine!
OK, I have the same problem discussed here. And I do have a file named Steam/steamapps/sourcemods/BMS/gameinfo.txt. But it is not on my list of games in Steam. I have restarted Steam many times, restarted my system…don’t know what else to do.
I did notice that the actual hl2 exe file is located in Steam/steamapps/myusername/source sdk base 2007 – is that right?
I used the default download paths, so I don’t see why any of it would be wrong.
OK, I copied the entire folder Steam/steamapps/myusername/source sdk base 2007 into the folder Steam/steamapps/sourcemods/BMS, restarted Steam to get Black Mesa on my game list, and this seems to be working! 
Have fun!
Doesn’t appear in mine either, restarted and reinstalled countless times.
Why the need to make it so complicated? If you can’t ge the installation right, what the heck is the game going to be like.
Don’t bother replying, game removed.
The Black Mesa team didn’t dictate the installation requirements, and their .exe installer was as straight-forward as it could have possibly been, it even detected that I have steam installed to a non-standard location. If you’re having this many problems with it then you’re most likely not reading the directions properly.
But, since you won’t reply, just a word for anyone else who might read this: Don’t be this guy, no one likes this guy.
What I did was run BOTH source sdk base 2006 and 2007.
This makes them appear in the username folder in steamapps, which in turn makes Black Mesa appear. Hope this helps
edit Oh and I started downloading HL2, dunno if that helped too