Blender wont render

I dont know why but whenever I use either blender internal or yafray to render it just doesnt work, all i see is a black picture. I even downloaded certain scenes used in tutorials to make sure theres no problem with the lights etc but still all I see is a black picture.

my first advice is to press ESC after a few minutes… it may be so that your computer doesnt work on the render and display it… i have a similar issue to that…
if its not that, then i dont know… do you have the latest version of Python installed?