Are you sure the keyboard num lock isnt coming on when it shouldnt - this happens on my old laptop. On some of the keyboard keys there will be numbers which correspond to this keyboard num lock. A combination of shift + something or ctrl + something will activate (and deactivate) this num lock so when you type the letter you want the corresponding number is displayed. Confused me for a while before I realised what was going on. May or may not be the problem.
Oggin