I do not want an editor. Thansk for the input guys, I tested most titles listed here.
SnagIt costs money. Fail.
Fraps I can use to make films, but I just can'T get it to take a single pic via hotkey - I hit the hotkey, put it takes no pic. Fail.
Greenshot opens a window even when I chose that it should save the file directly. Nice, but not what I wanted.
Irfanview does what i want, it saves directly withoiut opening any kind of interface - just that it does not accept the print-key as a hotkey. Why do so many programmers not know that these special keys still are valid keys? Almost the winner, but a single hair in the soup spoils it for me.
The winner is FSscreen. I hit "Print", and nothing happens. Afterwards, checking the main directory of it, the print is there. Right on the mark!