If some, or all, of the lights on one side of the display screen have turned off, but you can still see digits on the screen and the gun still fires, it could simply be that your battery is slightly flat and needs charging.
See "How much charge is left in my battery" for more details on how to check this. If the battery is flat, charge it up either by removing it and charging it with a mains battery charger. If you have a Bangalore Broadside Mode C with a solar panel, make sure the bird scarer is always positioned in the best place for the best charging. See "Where's the best place to put my Bangalore so the solar panel charges up?" for more information.
If the battery charge is ok (above 11.6V), there may be loose connections on the back of the board. See "How to reseat the connectors on the back of the board" for more information.
If you've tried the 2 above solutions and the backlights still don't light, the board may be faulty and we'll need to have it back so we can have a look at it. See "How do I remove the board and send it back?" for more information.