Your driver probably isn't installed properly. This is how I solved the problem.
Go to your Control panel > hardware and sounds > device manager > Ports
- then you should see "Unknown device". Double click on it
- Click on the "Driver" tab
- Click on "update Driver"
- Click on "Browse my computer for driver software"
- click "browse" and select the "drivers" subfolder in your Arduino folder.
- Click "next" and hopefully, your computer will install the driver for you successfully