Thanks twobob.
Yep the K3 root-filesystem
should take hours with Kubrick but it says it's done after a minute! But it's not as the Kindle won't reboot. Also takes an age to detect it before this. Nothing on the KK screen at any point.
After trying Kubrick I tried doing the manual noob debrick a la the Kindle wiki
https://wiki.mobileread.com/wiki/K3noobdebrickatk
D/Led the right files (i.e. for K 3.4) and followed right procedures but got a 'device not found on usb' error message from ATK despite trying different ports/cables and knowing they work with other devices (also Windows itself sees something it calls a 'Ringo something or other'! when I connect the KK to usb - but can't install it).
New battery also won't charge properly - orange light just goes off after variable period.
I'll look up the K3flasher prog.
PS K3Flasher seems to be only for Linux - I have XP....