To be really sure it would be best using the 10.10 Live CD and
then you'd know if it was just some incompatibility with it or the
upgrade from 10.04 ( chances are it will also work just fine but until
you check you won't actually know ).

Yes it would always be nice to fix a bad upgrade but apart from the
difficulty of finding out exactly what it is that's awry there's no
point even trying in your case if 10.10 doesn't work anyway !!!

FWIW - Badly applied OS updates have sent computing experts to the
funny farm trying to unravel and in reality the clean install is the
least hassle way overall. You could spend days or weeks fixing one bug
only to find something else rears it's head later ... ad infinitum


BTW - I discovered that the alternate install CD's have an option to
recover a broken install ( well at least the 10.04 LTS one does ). So
might be worth a shot doing a repair with the 10.10 Alternate Install
?