My keyboard misses letters and things when i'm typing..like the keys sticking but they not.

I can think of two things that could cause this,one is so help you god almost not worth it and the others pretty simple.
Not worth it:Your keypad sensativity could be worn out from over usage.This costs a lot to repair and mabey would be easier to just buy a new one.
Simple:Sticky keys.This key problem results from the shift bar being hit more than five times in a fast like manner.I had many problems with this while playing,N,way of the ninja.Shift was jump and I would keep getting sticky keys which would make my keyboard mess up.
If it is sticky keys you can fix it by making the sticky keys window pop up(Hit shift five times,fast like) and hit cancel on the window.All of the computers I have been on,which is alot,had the same problem and could be resolved by hitting cancel the second time through.Hope it helped

Change your keyboard