I've not used my Sp2 in a long time, I powered it up today and I was using the keyboard and the "I" key didn't work it lights up like the other keys and it presses down perfectly like the other keys but it just doesn't work.
I had something similar with my SP3 the other day : C and V didn't work.
I brought up the touch keyboard and they didn't work there either!
In my case it just some very weird software thing that was fixed with a reboot.