Is this a UK unit?
If it is, it sounds like you have it connected by Scart and RF leads.
In which case the scart connection is probably loose at either the TV or Video end.
The menu will activate the scart's AV switching and then try to connect to the TV's scart input. If the scart is loose, often either the video or audio connection pins do not make contact, so you end up with either a blank screen or picture with no sound.
Cobweb
October 2005