Try new batteries in your remote. If that fails I can only suggest that you unplug it from the mains and leave it off for a while - say an hour - and then plug it in again. If that fails you box may well be toast. Freeview boxes are so cheap now that they are not worth repairing. However if you haven't had it very long take it back to where you bought it ands ask for a refund under the Supply of Goods and Services Act.
Terry, September 2006