Given that the system is more than a decade old, reseat the backlight cable to the keyboard -- it's not unusual for them to come loose, or develop surface corrosion that prevents them from working 100%. Service manual:   [URL]
Hello! I am using Dell Latitude E4310.  .My problem is related to keyboard. I recently started re-using this laptop after 3 years. The keyboard lights were not working since I started re-using it .I used it for weeks and backlit keyboard didn't turn on  but yesterday ,when I powered on the laptop, the keyboard lights turned on automatically  and for the whole day they were working properly despite restarting the laptop twice or thrice. Now , today when I started the laptop, the keyboard lights are again not working .I have seen many solutions online , none of them worked for me. I have also updated my bios version to latest (i.e. A15).   Please help ! thx
Latitude laptop Backlit Keyboard not working