Digital channels are grouped together on Multiplexors ( Often called Muxes) which is why people tend to lose more than one at a time.
In my opinion your fault is almost certainly because your aerial signal isn't good enough. Second, quite frankly, you have bought a 'budget' price box and if you have signal problems boxes at the cheaper end of the market will be the first to show it.. (This is NOT a fault it is just how it is - a big Mercedes is more powerful than a Ford Fiesta.)
The fix is you need to get your aerial adjusted (or replaced) for a stronger signal and then retune the box to set up the channel list as though you had just installed it.
t
August 2007