Can you confirm that when you plug the Kobo Aura HD in, it is seen as a mounted drive in your file manager (Windows Explorer, Mac FInder)?
If not, there is something wrong with the Kobo/computer USB connection: maybe some setting/interaction you need on the Kobo?
My Sony relies on having the Sony Reader software installed before ADE can see the Sony, no need to run Sony Reader, just have it installed.
I'm not sure if the Kobo relies on other software (such as Kobo desktop) as well as ADE before it can be seen by ADE.
Maybe there is some issue with V3.1.0 and the Aura for some odd reason.
I'm afraid I can't think of anything else from the ADE end. You may be best seeeing if Kobo can help.