Gus, if the ereader shows up as attached to the computer with a drive
letter, but you can't access it with ADE, I have to 'assume' that you've
not registered your KOBO with their website. When you do that, KOBO writes
a small file onto the ereader with your ID and password in it. ADE looks
for this information in order to authorize the ereader.
When you register the ereader with KOBO, use your Adobe ID and password.
That makes things much easier when ADE goes to read that little file.
Hope this helps!