I have just brought an LG 42inc Full Hd Tv from Currys?

I have conected via a HDMi cable to Virging Plus Box , and also to an Xbox 360 , the TV Picure is very bad blocky , shadowy , shimmery etc just plain bad the HD channels are slightly better , the xbox picture is fantastic , had the guy from virging around changed the V+ box did all the test etc still no better , can anyone tell me if im missing a setting on the Tv etc...