OMG digging deep in an apple discussion, I found the solution! In the SPEECH control panel, somehow the key shortcut got set to my letter j! So if you are having the issue of a lower case letter not working no matter which keyboard you try, then this may be it! I already tried resetting all the keyboard defaults, resetting the preference file, everything.
I had similar problem except would not type capital letter "A" when you hit shift+A. My kids were playing with my laptop and had been playing with Speech function. System Preferences>System>Speech> Text to Speech; de-selected "Speak selected text when the key is pressed". Works fine now.
In response to simba's message, it works perfect! if your lower case keys arn't working and just the capital ones are, follow the instructions they have left and it should correct this! many thanks! If this fails to work perhaps try creating a new user account, open something that allows you to type text and hit the key that doesnt work, hopefully if this works then it will narrow down your search in respect to whether your keyboard button is working or not. Best
Thanks for the tip...I can now use my cap "S" again which was not working when I used shift and then s.The default for speech is shift-s. Actually bought a new keyboard thinking it was broken...anyone need a keyboard?
What the hell, I still don't believe that this was cured my problem too. My keystroke "d" is not working, originally, I think there is physical problem on the keyboard and is planned to buy a new one. However, this advise just cured that "D" keystroke.