If Windows Explorer ignores common keyboard commands
Sometimes Windows Explorer won’t receive some of the most common keyboard commands — no matter if you press the TAB button to change locations or select some folder, the arrows, escape… none of these works.
In such cases most probably the focus is on the Ribbon (File) menu. This means that to have your keyboard back to normal work, obeying the tab and arrows moves, just press and immediately release the alt key.
This way the focus is moved from the Ribbon to where it was the last time the keyboard worked on that folder.
If this won’t work, then you don’t have the ‘focus problem’, just use the TAB button to find your way…