Whenever I have problems with my Freeview box, I disconnect it from the mains for about 5 minutes and then turn it back on ... usually that sorts out any problems.
Mine's stopped working too, I have a Matsui one, I can get all the other chanels and have tried re-scanning and unplugging it, nothing has put the problem right.
Sorry to be of absolutely no use to you, but you are not alone in your TV viewing problems :0)