I've had one of these for a long time and over the past couple of days it will only let me see selected channels, mostly the BBC ones. Can't get ITV, Channel 4 , 5 and most of the digital ones.
I've made sure all the wires and aerial are connected fine and tried switching it on and off and rescanning it numerous times to no avail. It's always been fine before.
I would try and plug the Aeriel straight into the tv by-passing the freeview box and if you get the the terrestrial channels ok then it's your box that's at fault.
We had this problem a while ago when we bought a sky box without subscribing to their channels. The only way we could get these channels back was to buy a 'free to air' card or use the analog channels. As your free view box is old maybe you have a similar problem. If you look on the makers website maybe there are instructions to update the software.