Have you tried the drag & drop .reg file fix? (Nero 7 can break the registry if you install certain components; this fixes it.)
[Drag & Drop does not work for files or when customizing toolbars)
Installed PowerISO?
The fact that the My Computer problems happen in Opus but not Explorer makes it sound like something may be corrupting the Opus process (since Opus calls Explorer to generate the My Computer view, it should be the same in both programs). Thinking along those lines, I would disable shell extensions on context menus (as described here in the "Extremely Quick Fix" section) and disable shell image extraction (as described here in the "2." section.)