On your background layer, do you have the far right "bg" with a red cross on it or not? If yes, toggle it off and you should see it.
Also, depending on how your background clip was rendered, the very first frame may not show when you are the very beginning of the time-line(common occurrence when viewing clips in editing programs). Hit play and it should start showing up.
I know how it's irresistible to just jump into a new program without looking at the manual. But this type of question is something you can figure out on your own by checking the PI manual. That's what it's for :)