You would probably be safe then copying over your bookmarks.adr file and possibly a few other strictly-data files from the old folder to the new, but be careful not to carry in any sessions or operaprefs.ini files - they're some of the most likely candidates for conveying corruption from an old to a new install.
I had a similar problem, and it turned out that there was something wrong with its connection-related settings. Restoring an old backup of operaprefs.ini solved the problem for me.
(EDIT: Oops, did I accidentally necropost? Sorry - but I can't find a way todelete this.)