For my daughter's laptop --- Kubuntu 17.04 on an HP Stream: The keyboard has stopped working. The touchpad works, but striking keys produces nothing. This means we can't login.

Tried plugging in a USB keyboard. This also didn't work. She doesn't have a touchscreen so a virtual keyboard won't work.

It's as if any and all keyboards are somehow being blocked (or have been turned off) by Plasma.

I booted Linux Mint from a USB drive and the keyboard worked just fine. So... this isn't a hardware problem. It's strictly a Kubuntu or Kernel(?) problem. Any ideas? I'm at wits end.

Okay. Using recovery mode, I'm at a root shell prompt. Keyboard works fine. This is definitely a Plasma problem.

Any help would be greatly appreciated.

What system files could I reset, reinstall, delete in order to "reboot" the keyboard?

same here

hey men try

Try whether the keyboard works when passing the kernel "pci=noacpi or acpi=off" (edit the grub entry at boot)
If yes, it's an ACPI issue (and you should seek for a less broad approach - the upper will loose you battery load status and probably keep the fans at max)

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from luebking
it works for me