Kobo Aura H20 - not being being read a device to authorize?

I've download Adobe Digital Edition to my PC, I have authorized my computer, I have downloaded the library book to but it's the only thing I see?  I have plugged in my Kobo Aura H20 (which is included in the compatibility list) to the computer. BUT, it doesn't appear in the list on the left of as a device so I can't authorize it.  Why doesn't appear?  And how can I authorize it?

Thanks

K