You've likely messed it up more at this point by pointing to the wrong directory on your system for .jar files. Enter the following to take things back to where they were when you started:
ftype jarfile="C:\Program Files (x86)\Java\jre1.8.0_66\bin\javaw.exe" -jar "%1" %*
If HD is starting (giving the loading image) then your problem is not with file associations. Create a new thread and post the contents of the trace.log file from the directory that you installed (unzipped) the HD download into.