Let's get Darkness Falls installed, then we can go over how to install the HDHQ modlet into it.
Can you re-launch Darkness Falls mod, and start a new game? Once it's started, you can close the program. Back in the Mod Launcher, click on View -> Log Files, and select the output_log.txt in the drop down box, and click on Upload Log file. Copy the pastebin.com link here, and we'll see what happened.