I changed the environment variables thing like suggested in another thread, and I validated the game files, but I still can't get Hammer to launch. I'm using the .bat in the bin folder like I think I should be. It worked fine yesterday, but now it just won't launch anymore. I also kinda need it to work, since I'm making a TF2 map for a school project. Does anyone know what might be causing this, or how to fix it?
Go to the betas tab for tf2 and try the prerelease version. Also make sure your using the hammer in your steamapps/common/team fortress 2/bin folder
It turns out the .bat doesn't work anymore (for whatever reason). I just used the Hammer.exe in the bin folder and now it works fine.