If you play a video on a Windows PC you can't take a screen shot. Press Print Screen won't give you anything. If you use Greenshot or other screen shot utilities, again you'll get nothing, just a black screen! Then I came across the solution. I'm using VLC Media Player and I noticed it actually has a built-in screen shot function!
In VLC Media Player, play your film, press pause at the screen you want to capture.
Click Video | Take Snapshot
An image file (PNG) will be saved in your My Pictures folder.
Change the default save location
To change the default save location click Tools | Preferences
Click Video and change the 'Video snapshots' Directory (click Browse to select a folder)
For this change to take effect you must close VLC Media Player and re-open it.