I never knew it was the led. I would just place my hand over the top of the device to get the keyboard to light back up. Guess that's why it was hit or miss for me.
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i put my hand over the led and nothing. but like i said when i do a battery pull it works when everything loads up. then nothing. sometimes it works sometimes it dont.
Go to Options > Screen/Keyboard > Auto Dim Backlight. Verify it is set to On. If it is, then there is most likely a software conflict. You could possibly resolve it by reloading the OS.
Mine does this from time to time. I figure often it has to do with the amount of light in a room and is not always necessary to light the keyboard. But if it is doing it it almost total darkness then there would seem to be a problem. Check settings and try hard reset like others have mentioned.