First ensure the connection of the sky cable to your box is secure at the rear of the box. Otherwise/also...
Try a forced software download...
1. Press & keep held down the 'BACK UP' button on the Pace front panel.
2. While holding it down, disconnect & reconnect mains power.
3. Keep 'BACK UP' button depressed until all 4 lights illuminate on the front of the Sky receiver, (also a message will be displayed on your TV screen).
4. Only release the button when lights illuminate (approx 30 seconds after reconnecting power in 2. above).
5. The box will be updated with latest software version. THis takes approx. 10 mins.
6. Box will return to standby on completion of update.
7. Leave in standby for 1 min.
8. Switch on and wait for channel list to be updated, approx 5 mins.
The above often cures erratic operation such as you are experiencing.
Cobweb, December 2005