Solved: can't type in XP

hi i cannot type anything in my XPpro desktop, the alt key does not appear to be stuck, the keyboard is a wired microsoft and seems to be fine.
i run a paid for version of zone alarm as my AV plus a free version of key scrambler, both have been temp disabled with no good result.
the problem has been around for some time , i have previously fixed it by system restore but that does not help anymore.
i believe it may be a` corrupt or damaged DLL file, there are programs available to repair these but as i cannot type anything how do i instal them in my computer.
any advice appreciated, thanks patsym: