The bottom oven switches off - how can I fix this?

Hi,
I have a Baumatic B904SS Built In Double Oven.
The bottom oven switches off by itself when I try using it, so have had to resort to using the smaller top oven. The light display unit comes and goes, too, when I'm having this bother.
Is there a loose connection somewhere? Sometimes when I bang the door shut, the digits light up and the oven somes back to life.
Hope someone out there can help!

Thanks,

Jill