WE saves screenshot in targa format, and not all of them... I'm really frustrated how it actually works.
When hitting printscreen your WE should pop up message like "Picture taken" in the middle of the screen. If message did not appear, that's the problem, either your button doesn't work, or it has to be clicked with another one, like ctrl+prtscrn. Your pic is now saved somewhere inside a computer and will be held there until reset. Go to paint, photoshop, any graphic redactor and find "paste" button in menus (ctrl+v is just a quick hit). I really don't know where the problem is, possibly somewhere between the screen and the chair.