Kobo ARc does not communicate with PC

I read the manual and tried all suggestions made (for Kobo-readers) here but still my computer nor lapton recongises my kobo arc as a usb data-device.
It's frustrating to have a brand new tablet/reader that does not cumminicate with the computer.
I only can update data via the alternative of 'dropbox'.
I already updated the computersoftware.