Freeview problems

Hi there,having a problem with getting all the channels on both tvs in the house coming up saying no signal or invald channel even after updating the channel list any idea on what is causing this? before we call in the experts.
Can only get tv 3 and 4 in good picture but everything else is blocks or no picture at all.

do you have a box that records? if so you can only record and then watch another channel that is in the same group. I don't know what channels are in which group, but I will get the message invalid channel if trying watch the wrong channel at the same time as recording something

yes we have a hard drive recorder with freeview as well as the tv with freeveiw built in

If it is only doing it when recording, then that is most likely the issue. I am sure google will tell you what channels are in what groups. If it is doing it all the time, I haven't got a clue OH, probably would though.