Try the following procedure on the remote control:
1. Remove batteries
2. Press the buttons repeatedly to ensure no buttons are stuck down.
3. Leave the remote control for a couple of minutes
4. Insert the batteries again and retry
If that fails, try cycling the power as follows:
5. Remove power feed to STB for 30 seconds
6. Plug it back to the STB
7. Switch the STB on
8. Try again.