This has been happening to me, too! I was considering asking this very question. Computer techs checked and said computer was clean---got it back home, and had missing letters all over again! Called them, and they said it must be a bad keyboard. Replaced that, still no change. It's very irritating, and so s--l--o--w! Has been happening for about a month or a month and a half (?). I keep doing Norton maintenance chores, which sometimes help a bit, sometimes not at all.