Hello! Thank you for reaching out to us. I am the Dell-Cares contact only for Order or Sales related questions. For all Technical Support issues, you need to contact the Get Help Now support team Monday through Friday. Moving your thread to an applicable hardware board. Click the Get Help Now on right to start a chat.

Reset the EC controller.  Unplug the system, remove the base cover and disconnect the battery from the mainboard.  Hold the power button for 30 sec.

Reassemble the system and plug it in.  Power up -- it will take 2-3 cycles to get the system powered up.  See if that restores the backlight function.

Good suggestion from ejn63 on the EC reset — worth trying first since the embedded controller is what talks to the keyboard backlight. One more thing to check: boot into BIOS setup with F2 and look for the keyboard illumination setting under the Keyboard or miscellaneous section, because some BIOS revisions flip the backlight off by default after an update. Also try cycling it in Windows with Fn+F5 (or Fn+Space on some Inspirons) — if the toggle doesn't even appear, that's a good sign the keyboard isn't being detected as a backlit part. And it's worth verifying your exact configuration by service tag, since a few Inspiron models shipped with both backlit and non-backlit keyboard options, and a mismatched EC/BIOS profile after the flash can hide the option entirely.

What is the exact model of system that you have? Is it possible to roll back the BIOS? What version was installed? 

@ejn63​ I have removed the battery and pressed power for 30+ seconds.  No success.  The BIOS still does not list a setting for the keyboard.

@DELL-Daniel V​ My laptop is an Inspiron 5559. The bios is 1.9.0 .   Not sure if a rollback is possible.

@noahmitchell​ Thanks for your input.  The BIOS does not have any setting for the keyboard.  I've had this laptop for years and the backlit keyboard has always worked.  Now, after updating the BIOS not only does the F10 backlight key no longer function, the BIOS no longer has any settings for the keyboard.

@PBILLS​ 

You can try reseating the keyboard connector to the mainboard to see if that helps.  If it doesn't, it could be the keyboard itself that's the issue or the keyboard connector on the mainboard.  At 10+ years old, any parts replacement needed should be evaluated in light of the value of the system - probably $50 or less complete and working.

@PBILLS​ Given the age of the model, its unlikely to be a known issue with the BIOS version since it was released way back in 2020. I don't see any notes indicating that you can't roll back, so you could try to go to 1.7.0. I would probably load the BIOS defaults first though to see if that restores keyboard options. 

@DELL-Daniel V​ Thanks for your help.

I had tried the BIOS defaults with no success.  

I just gave 1.7.0 and it failed with the message it was an "unsupported downgrade".