Try doing a rescan. I lost them a couple of times on my LG and a rescan bought it back, but in the end the giant banner was so annoying I turned it off again in the menus.

Someone may have also turned it off because of the banners.

ubernoob: Looks like 'have you tried turning it off and back on again ' works for freeview too.
I turned it off at the wall and have on demand back

We all know this is the correct response to any IT/tech related question!