installed Nero 7, worked ok.
next day i ran registry mechanic.
next day, cd & dvd drive are missing.
device manager reports registry error (code 19) with missing drives.
searching on web, this is a know issue with some software, but following microsoft fix ( Remove the Upperfilters and Lowerfilters values completely from the following registry key:
this dose not resolve the issue.
roll back changes made by registry mechanic, same result.
roll back to before nero 7 install. problem solved, cd & dvd drive back.