Could you try pressing the command key and using the 1 and 2 keys to see if you can adjust the brightness of the display so we can see if it is the function of the keys or the keys themselves that are having issues.
Let us know
The command key + 1 and 2 had no effect on the brightness. Some added information: The disc drive key is also not working. I had checked the ribbon connector for circuit breaks, but didn't find any. I now recall that I had an extended power outage in time frame that the keys suddenly stopped working.
Could you shut down your machine then power it backon and as soon as you let go of the power button press and hold the SHIFT key till the load icon appears under the Apple icon, Then release the shift key and wait 5-30 mins till your machine safe boots then just restart.
This way we can see if your machine is not responding at all, Plus the Safe boot may help.
Let me know what happens.