I tried that, re set up everything. Calibre now will talk to the kobo.
Re-put on all the books from calibre to kobo, I checked that I'd sorted them all first.
Kobo is still not showing the books I've put on. 13 books but nothing showing on the machine.
Again, I plug it in, and open the files on kobo - there the books are.
I am at the mercy of a furious parent, is there anything I can do?
eta, just plugged it in again, opened calibre, clicked 'show books in main memory of the device' and they show up there.
Just not on the damn reader itself