Some channels not working on my new Freeview Box?

Just bought a new freeview box and have found to my total dissappointment that I don't seem to be able to get many of the channels while others work absolutely fine. 001 - BBC1 - Works 002 - BBC2 - Works 003 - ITV1 - No Signal 004 - Channel 4 - No Signal 005 - Five - No Signal 006 - ITV2 - No... show more Just bought a new freeview box and have found to my total dissappointment that I don't seem to be able to get many of the channels while others work absolutely fine.

001 - BBC1 - Works
002 - BBC2 - Works
003 - ITV1 - No Signal
004 - Channel 4 - No Signal
005 - Five - No Signal
006 - ITV2 - No Signal
007 - BBC Three - Just get the info screen so not sure or not
009 - BBC Four - Just get the info screen so not sure or not
010 - ITV3 - No Signal
011 - Sky3 - Works
012 - UKTV History - Works
013 - More 4 - No Signal
014 - E4 - No Signal
015 - ABC1 - No Signal
016 - QVC - No Signal
017 - UKTV Gold - No Signal
018 - The Hits - Works
019 - UK TV Brt Ideas - Works
020 - ftn - Just get the info screen so not sure or not
021 - TMF - Works
022 - Ideal World - Works
Other info is I'm in a Freeview Zone according to freeview.co.uk (3 miles outside Manchester city centre) and house was built 2 yrs ago so would assume they put in all the right gubbins for digital TV reception
Update: Just to confirm - the first thing I tried was to rescan for all channels - it told me it found some new ones but the channels above are those available after the scan (I stopped after a few or I'd run out of space!!)
Update 2: I hope I don't have to do anything with the aerial as I live in a block of apartments and the aerial I guess is stashed up somewhere that I can't easily reach
Update 3: Just tried totally resetting everything : now the channels I couldn't get before aren't even on the list and the ones I could get are coming up as Audio only channels. :(
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