hldj.org

1) Does HLDJ launch the game correctly for you? Yes
2) Does "HLDJ Loaded Successfully" appear in console on starting the game (with no errors)? No.

The normal version worked fine with L4D2 for a long while (After all the DLC updates) and then at some point stopped working. I checked it with Team Fortress 2 and it works fine there, and I've tried the L4D2 fixed version of HLDJ with no success.

Any help in this would be greatly appreciated.

Thanks in advance.

read through this sticky: http://hldj.org/forums/viewtopic.php?f=5&t=680
there's steps to find your game directory, your game audio directory, the config input directory and config output directory. that will give you a clearer idea of which directories to use.