Just discovered that this option - 'Factory Menu' - on my camera isn't one that I should be seeing. I didn't think anything of it when I got the camera and accessing it opens up a huge amount of technical mumbo-jumbo that I've kept away from. And, not having had a look at a similar camera, I assumed this was a standard menu option.
It came to light when I got myself a wireless remote recently and couldn't get it to work. A trawl through the Canon support and third party forums and I found that this menu is something that's only used during servicing and should be reset before handed back. Unfortunately mine's wasn't and it needs to be taken to a servicing centre to be reset.
I've had the camera for 16 months now and it's not caused me any issues until now; it's the reason the remote doesn't work and also means I can't connect the camera by USB to the computer.
Anyway, I've contacted a service centre now and will drop this off to get fixed. Hopefully it won't take too long to remedy.
- Canon PowerShot A710 IS