It sounds like someone has installed a keylogger onto your PC either remotely via the net or manually by letting someone use your PC, I would recommened a full virus & Spyware scan, then go to add and remove programs and look for anything you have not installed, by the way some keyloggers do not show up in add or remove or in the program folder, they usually hide in the system32 folder under a differing name, I would strongly advise you not to go into this folder, but to take your PC to a qualified CISCO or MICROSOFT engineer who will be able to give your PC a full diagnostic and hunt the keylogger down.