When rendering the render shows up grey

Hello I was looking for some help with rendering whenever I try to render out what i’ve made it turns up grey
Just like so: http://gyazo.com/f5af654d5cca13b1b083abaeda1fdc76 I’ve looked it up and can’t seem to find anything on it so I was wondering if anyone could help me with my problem.

Hi, hard to say without the file but you have unchecked some of the cylinders in the outliner.
You can get them back with Strg+Alt+H or check them manually.
If render work with the default cube may upload the file > pastall.org/blend

Cheers, mib