I've also seen this, and like Rob, the solution seems to be a cold restart
(turn the power off).

For the benefit of any experts who might care to jump in with an explanation
of the cause, I've seen this on the following system:

--WinXP Pro, sp2
--2 user profiles, with fast user switching turned on
--no password set for user account
--system wakes from standby (not hibernation, which has been disabled) with
"system is locked; only admin or <username> can unlock" dialog box with
userid correctly filled in and one character (dot) filled in in the
"password" box
--no responsxe to any keyboard input (can't make any changes to "password"
and can't use control-alt-delete)

"Rob" wrote:

> It happened to another user I know he rebooted his laptop & it hasn't
> happened again since.
>
>