Thank you, JS Wolf, for the suggestion that the USB port needs to be replaced. But surely if it were defective, the Kobo would not recognize the computer. But is does when it is connected by USB cable. As I explained, when I connect it by cable to the computer, the Kobo screen immediately changes and shows a computer. This change is brought about by the connection. Also, before the reset, the Kobo always recognized the computer and presented the menu to connect or not and announced that it was connected and charging after accepting the connection. The problem is that the computers do not recognize the Kobo....
But perhaps there is something here that I do not understand.... more advice is needed!
