To restore your default settings, delete the file(s) "opera6.ini" in your profile directory. This can sometimes solve problems you are suddenly experiencing.
If you want to start fresh with Opera, you may delete or rename the entire profile directory. Remember to take a backup of things you want to continue using, such as bookmarks ("opera6.adr"). If you simply rename this directory, you can always find your old configuration files here.
Need help? Hit F1 anytime while using Opera to access our online help files, or go here.