@Neemobeer. You were close.
I got it solved.
I hit alt+tab until the Windows explorer window was the front-most window. Then I hit alt + pressed Space, let go of both and hit M, then used the arrow keys to move the explorer window back on-screen. Because I had 'Extended desktop' in my Windows' Display settings, it was off-screen.
It went off-screen because I used to use a second monitor but then later on I didn't use the second monitor anymore and turned it off but you can still accidentally click and drag open windows on to it.
So I used the arrow keys to get the window on the visible portion of the screen. Thanks!