In this case I would download iobit uninstaller http://www.majorgeeks.com/files/details/iobit_uninstaller.html
Run it and uninstall Opera run the powerful scan after to delete any leftovers, then reinstall Opera from scratch. Make sure to back up your bookmarks and whatever else you want to save.
Otherwise just try renaming this file operaprefs.ini, usually in your profile folder, to operaprefs.ini.back with Opera closed. Then open it. It will act like a new install. Again backup before doing anything and this second method only works with Opera 12.xx or earlier. I don't think it will work with the newer versions.
Just a few things I would try.