This might be catalogued as random stupidity from my part, but Binging for it didn't really bring me to the information so here goes. I'm currently working on a 3 year old laptop that has been travelling with me pretty much around the world. 16GB, Core i7, 2xSSD, it never lets me down. Yesterday while I just stepped off the plane and arrived at the customer, booted my pc and cleaned up the inbox something strange happened. All of a sudden my keyboard stopped working. Everything else worked fine, but typing just wasn't happening.
EDIT: One of the comments mentioned that [Windows Key] + [Spacebar] should be the quick fix for this problem. So try this, before reading further.
As any highly trained IT professional I of course resorted to the one and only possible solution to fix this: hitting every key on the keyboard, with the same "schwung" as professional piano players go from the low note to the high note. And to my surprise at times there was a key popping up. So maybe it wasn't the keyboard. Again, I am a highly trained professional, so solution number two: reboot. In all honesty, this would be the first time that I actually had to reboot Windows 8 to get something to work again. Reboot, the bitlocker unlock window comes up, I type in my code and the keyboard works fine. Problem solved. Logged in to windows, and the same problem comes up again.
No worries, I am still a highly trained professional so I open OneNote and after my piano move I resorted to option three. Push it until it works. I just pressed a key for a long time and to my surprise the character appeared. So I went to the keyboard settings for the repeat speed, but changing that did not resolve it. There was only one thing I could still think about. Ease of Access settings. And there it was: The filter keys were enabled. I don't know how I did it, as the settings were still set to show a warning when the Filter Keys are enabled, but for some reason I did not see the warning or I pressed Enter when it came up without realizing it.
So when you are in the situation of your keyboard no longer working in Windows 8, press a key for a long time and see if it comes up. If it does, that it is probably the filter keys. To go to the settings, press windows key for a long time (filter keys is on) till you get the metro menu if you aren't there yet, press f for a long time, press i for a long time... (you get what the other actions are...) until you have put in Filter Keys in your search window. Click on Settings, Ignore Repeated Key Strokes using Filter Keys and untick Turn on Filter Keys