No bootable device -- insert boot disk and press any key

I've had my macbook pro for about to month now. I've had not problems with it until today.

Every time my computer is restart I get the message "No bootable device -- insert boot disk and press any key" I have to restart hold down the option key to select my hard drive...

How do I get rid of this message?

 

Thanks that seemed to do the trick... any idea why it might have be doing this?