If you have this problem on your Windows 10 computer, chances are your computer has accidentally switched into Tablet Mode the last time it rebooted.
To immediately fix the problem, click on your Notifications button found at the far right of your taskbar. You will see a number of features that can be turned on and off. Make sure the “Tablet Mode” button is off.
To assure this doesn’t happen again, go into Settings > System > Tablet Mode.
The very first setting will probably say “Automatic” or “Use appropriate mode for my hardware”. Switch this to “Use Desktop Mode” if you are on a desktop or laptop. Switch it to “Use Tablet Mode” if you are on a tablet. Only use the automatic mode if you are on a device that can be used as a computer or a tablet.
That should solve your problem.