Have you restarted the computer? I can get the USB ports to a state where the device detects it but the PC doesn't. Rebooting is the only thing that helps.
You can also try
USBDeview. Find all the references to Kobo devices and delete them. Then reboot.
And if you have another computer, try that. If it isn't working there, you might need to consider a factory reset. Or it might be a problem with the port on the device.