I honestly had this same problem, heres what I did to fix it..
First of all, open up the installer you downloaded, click uninstall.
After you uninstall that one, I went ahead and got another installer, ran it as admin saved it to its own folder on my desktop.
Now, i put my WoW in windowed mode, and i used the actual Battle.net launcher ran as admin to start it.
Go ahead log into WoW and fire up hb and dont play with any settings, just use it how it is and see if it works, then slowly play with the settings you want. Personally i found that when i turned on the auto scroll/buff feature thats when my fps went to the floor.
The problem with me was when i was in combat i was fine, but out of combat my fps was horrible. Hopefully this helps!
** FORGOT TO MENTION : Make sure you run HB as Admin as well **
If this doesn't work then I have one more idea for you but please, the key thing is dont fuck with anything off the start until you know if its working correctly, then ease into it. People get carried away sometimes.