I would love to use Opera because It has some very cool features.
After reinstalling windows, remove and reinstall the browser… back up opera settings is very necessary.
I have found it a very useful tool: Stu’s Opera Settings Import & Export Tool.
Stu’s Opera Settings Import & Export Tool is developed explicitly to take much of this hassle away. This tiny piece does hell of a job in backing up and restoration of your bookmarks, mail, contacts, sessions, preferences, etc and enables easy transfer of them between Opera installations in different folders or drives. It also remarkably restores the settings if they appear to be lost.