Really??? I have this problem!
Check that the Kobo is recognized by the computer in your file manager (windows explorer, mac finder).
If it is plugged in and turned on and does not show up as a mounted drive, the problem is either on the Kobo or with your USB cable/port.
If not, try a factory reset of the Kobo and try again.
No point in trying anything with ADE until the Kobo shows up as a drive.
If the Kobo shows on the file manager but not on ADE, try the older ADE.
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Some people have found ADE trying to upgrade automatically.
It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run.
Probably best to say no if 2.0.x installation asks if you want to migrate your library.