Can you un-install Nero (both Versions)?.
From Explorer goto TOOLS and open VIEW, selrct the options to see all SYSTEM and HIDDEN files.
Search for *.bak files with the NERO or AHEAD name and remove.
Try to Reload Nero 6 (or re-load a fresh copy of NERO 7 from the NERo site). If this installs --Problem solved, if not repeat from start,except for re-install), goto REGISTRY ,FIND and look for all NERO / AHEAD entries and remove.
WARNING-- Before you edit the registry make a back up (EXPORT) in case of errors.