Sorry if this has been covered elsewhere, but I found nothing similar. One of my machines all of a sudden is rejecting my wife's password as user

. After she hits the "enter" key for her username and start typing her password, instead of seeing one symbolic character for each letter she types (like "*"), she sees three ("***") and of course login fails. A defective keyboard as a possible cause has been already ruled out. This is one of two machines I upgraded from F9 to F10 by means of preupgrade, with minimum problems. The other upgraded computer is doing just fine. Any hints?