It may sound crazy, but it happens. Some times a fuse (I'm saying the glass, tubular type with the silver ends) break below or above the glass, hidden by the metal. If you use a continuity meter you'd be sure if it's good or failed. As to the more modern fuses, they're pretty obvious when they're broken. Of course, replacing either with a new, known good fuse (your spare - ahem) would be a simple check for that situation. If this isn't a solution, it might make us think a little different. By the way, don't use foil gum wrappers to "bridge" a fuse. Well, there's my two cents worth. Best wishes.