Try booting to safe mode. If it works in safe mode it's possible for a few things to be in play.
1. Keyboard mapping.
2. Key logger. (few key loggers work in safe mode)
If that clears it up scan for key loggers and look at key mapping.
i said computer because i switch for a new keyboard.. and the same problem happen.. i only cant type the letter "z" on both new and old keyboard.
but the funny thing.. i can type my computer password who contain a "z".. after that i cant type it anywhere
Funny isnt it ??
Can someone help me with this !! its not the most popular letter.. but i need it !!
thx in advance !!