If you need video screencaps, here’s two options.
1. If you have Windows Media Player, and try to use the Print Screen feature, often you end up with the “black screen problem,” where the video just isn’t there! This is caused by overlays. To disable them, go to the Tools >> Options menu. Under the Performance tab, there will be an “Advanced” button. Hit that, then uncheck “Enable Overlays.” There you go, you can take screencaps! (And if you can’t understand these, check out this)
2. If you don’t use Windows Media Player, you can always check out VLC Media Player. As well as being a great all-around media player, it’s very easy to take screenshots — when you right-click the video image, it’s there. Being an open-source enthusiast, I would highly recommend this alternative.
There are also various programs that take screenshots, but I’m tired and can’t think of any right now — but feel free to post in the comments.