Another two synonymously used tags: All 4 questions tagged hard-reset deal with factory-reset (x67). In fact, except for one they are even tagged factory-reset additionally.
I'd suggest to merge those four questions into factory-reset, and optionally make hard-reset a synonym to factory-reset. Though Matthew may be correct that a "hard reset" originally might have referred to "hard reboot" (by removing the battery) -- everywhere I read about hard-resetting a device, the procedure decribed was in fact a factory reset.
Merging would be as easy as removing 3 tags from their respective questions, and just change a single one I guess ;)