My alt key doesn't work on any keyboard, even Windows onscreen virtual KB

[Janeiac]

Also F10 doesn't work.
When I say "doesn't work," I mean no scancode is issued. I checked this by using the "type key" button on sharp keys that picks up a scancode for you to remap (without actually rewriting the registry to do the remap or saving anything.) I tried to remap from left alt to left alt by using the available list on Sharpkeys, but that didn't do anything.
This problem occurs on both a PS/2 old IBM model F PC and a brand new Logitech cheap USB rubber dome, and on the Windows onscreen virtual keyboard.
I'm running Windows 8.1 on a brand new homebuilt PC
All the other keys seem ok.
Any ideas?

[blackbox]

Have you tried any of the suggestions in this link?

http://windows.microsoft.com/en-gb/windows-vista/troubleshoot-keyboard-problems

[Janeiac]

Yes. 1) The solution is for Vista and I'm on 8.1; the "fixit" wizard won't run. 2) none of the info on that page addressed my problem.
I've searched the 'net and haven't found anything useful.
I'm thinking driver issues but all I can find is the generic MS PS/2 native driver. Is there something like the MS Intellitype driver that would work for me?

[Findecanor]

I have heard about some graphics card driver having a settings program running the background that allocated some keys for its own purposes. I can't seem to find that old post to see what it was, sorry.

Do check which programs and services are running.

[Janeiac]

Thanks for the suggestion. It's a brand new build, so relatively little has been installed. Any idea which service may be suspect? What should I look for?
One issue was that when this machine was first set up, it had a USB keyboard. When I next turned it on with my PS/2 keyboard, the keyboard was not recognized at all, not even in BIOS. Some searching revealed a known issue in which Windows disables PS/2 support if a USB keyboard has been attached. The fix is a registry edit to restart the service i8042prt. I wonder if this is somehow related? Perhaps something with that service?
This machine is using onboard graphics.

[rowdy]

Is it feasible for you to reinstall Windows?

Just wondering whether something is totally screwed up, and you could keep guessing for months and not find it, or just reinstall from scratch and MAYBE it will just work.

[da20valve]

Change your keyboard layout and try both the left and the right ALT keys, you will find this should work

[Janeiac]

Did you mean change language or to Dvorak? I changed to French. Still no alt key, then back to English. Still no alt key. Rebooted in between.
Did you mean something else when you said, "change layout?"

[dorkvader]

I would see if it's the computer hardware or the keyboard.

Sometimes, if a key is "stuck" it will be disabled, this could explain why it's not working on the OSK. Try it on a different computer.

Also try to see if it's an OS issue or something else, Try booting to a linux livecd or liveusb and seeing what happens.

[Janeiac]

It's not a stuck key. It's not the keyboard. I tried 3 keyboards, and the onscreen virtual keyboard. No scancode is issued. It's clearly a software problem.

[Janeiac]

Further investigation reveals that Windows 8.1 itself is swallowing the alt key scancode; certain Windows-blessed programs, such as Word and Wordpad, that have defined actions for alt key combinations just as alt-s for save as, do receive the keystroke. What seems to be happening is that Windows it itself swallowing the keycode and issuing a Windows event. If an application doesn't read the Windows event, then it appears no key at all was pressed.
So, I can still do what I need to do, just not the way I had expected. Thanks to all who offered suggestions.