your vid screen is set to 72dpi, if you have rendered to a new window at a higher res ie300dpi you should see a slider on left side and a slider on the bottom of the window. you need to adjust these to see parts of your image.you won't see all the image at once, the screen cannot display it.
that's the limitation of most ( if not all ) lcd and crt screens. even HD doesn't come anywhere near 300 dpi.
hope this helps