Its now July 2017 and teh LED issue was same problem for me - now solved. FANTASTIC - thanks a million times guys.
FWIW I had exactly same problems with my keyboard on a Sony Vaio Model SVF15N1C5E on Win 10pro - started in December 2016. Backlight would come on at startup but keyboard dead after that. Had to use on-screen k/board or USB to log-in.
I had tried all usual driver updates, Win10 updates, install/uninstall in Device Manager etc - all not worked. Took it to local PC shop about 6 months ago and they said keyboard not showing in BIOS (I haven't checked) and thought m/board possibly on its way out.
Been using USB keyboard for 6 months as not wanted to spend any more on old laptop. Occasionally, CAPS light on laptop keyboard would light up when using USB keyboard but intermittent.
Then, about 3/4 weeks ago, laptop keyboard suddenly started working again for no obvious reason. Last week it went dead again (Grrrrrrrrrr!!!!!)
Spotted this thread and opening up the back and fiddling with the LED board solved the problem. In my case, I was just reviewing things with the back cover off and the battery still charged & connected(!). I thought I might be able to disconnect the LED connector without the hassle of taking out the battery and as I was faffing about with the purple ribbon cable connector the red LED light came on.
I left the LED board connected, replaced the cover and re-started. Keyboard is working fine now and laptop has been powered-down and re-booted from battery and mains power 3 times each.
Also noticing a quicker boot-up time.
This was driving me insane - thanks, thanks, thanks, again.
Andy