Ok the plot thickens.....
Today I've spent a few hours trying to get this Pod Go to re-awaken. Following the advice in the Line6Tony video above, along with some almost identical instructions from Line 6 support, this is where I am.
I uninstalled everything Line 6 from my PC and restarted the PC.
I downloaded Line 6 edit, the drivers etc from scratch along with Line 6 updater.
I booted the Pod Go into update mode by holding down page > (right) whilst turning on. THEN I connected the PG to the PC (this does seem to make a difference as I'll go on to later)
The good news is that the updater software now sees the PG. I tried over the course of a few hours to load up various versions of the firmware, but each time the update starts but then stops and I get an error message! It seems to want to load but crashes every time. I've had no better success trying to load v1.1 than v1.3 - it doesn't seem to make any difference.
I've found that disconnecting and turning everything off helps to get the update started - if you leave it connected, or don't restart the PC even, the update doesn't even get started before it crashes. It's also worth pointing out that I have nothing else running on the PC at all, and no screen saver or sleep mode kicking in.
So, I'll continue trying, but am losing faith by the minute! :(