[racket] how can I save screen to a file?

Hello, I am using DrRacket on Windows 7
I wonder how can I save screen to a file.
There might be some ways.
the way I tried is
simulate PrintScreen keystroke
and save clipboard to image file.

referring to racket document,
I tried
(define ke (new key-event%))
(send ke set-key-code 'print) or (send ke set-key-code 'snapshot)
but both effect nothing.
I can't paste anything to paint program.

do you have any advice?
thanks