menu disappeared

Hi I used this theme for my website and love it. I am rarely on my site but popped on the other day and the menu bar has disappeared. the settings all indicate that it should be there and all the pages are there but no show on the menu bar. I have not updated or changed anything and am running few plugins – it not much more than a text based site with a twitter feed. I’ve had to change the theme right now but am keen to know if I’ve missed a setting or if this is solvable?

Many thanks.