I'm stumped. Can you send me a download link to your .blend file so I can take a closer look? Easiest way is to upload to dropbox, google drive, or equivalent cloud storage service and paste a download link to it here.
Ahh ha! It's because you're camera is zoomed way in and all that's visible is the grey plane, appearing to be a blank render. Just move the camera around and you'll see the scene rendering (dull and grey, but rendering nonetheless)