OK, I had a burst of enthusiasm and read a bunch of articles exhorting me to try different USB cables and ports on my computer with the reflasher, before chucking this thing in the trash.
So I once again opened the Zero to replace the original SD card before trying to flash it again.
And the battery wires pinged off the circuit board. RAGE!!!!!!!
But because I randomly have a soldering iron, I managed to fix it!!!!!!! I AM A GOLDEN GOD!
And then re-ran the flasher rescue USB stick. And it came up with the dreaded red "Flashing Failed" message.
And so I changed the USB port and cable (not that everyone has many USB mini leads!). And it INSTANTLY said "Flashing Failed".
And then I thought that maybe every time it says "Failed", you have to do the whole UNPLUG-HOLD SELECT-RESET-RELEASE SELECT-REPLUG dance. So I did that.
And I requested a FULL reflash. And it got to "Probe 1th", waited a bit, and failed.
And then I tried again.
AND IT WORKED!!!!!!!!!!!!!!!!! Green light is back, system is back working!!!!! Time to reinstall my stuff....... WOOP