My digital TV and box only picks up BBC?

Hi all,
I have a TV with a digital box built in. Sometimes we can pick up all the channels on the digital box but most of the time we can only get the BBC channels. I have a diagnostics button and it says signal 46% quality 98% on the bbc channels.

Seems to get worse when weather is bad, like most of the time of late!!. We are with virgin and only have broadband and phone, NO TV. we have a grey box outside whch is like a nest of worms. I cant work out if the airel is connected and where it is connected to but as the problem is coming and going I am thinking its connected ok.
Any help or advice i would be grateful.Thanks

bb
January 2010