>thanks Naomi,
>
>I have tried all of them but none work.
>may be it's difference issue.
>
>regards,
>
>Jerry
>>You can use API to LockScreen. See Re: Lockscreen does not lock Thread #1338795 Message #1338854

Last time I tried it I can not do anything in the form. But of course I can switch to other windows and work.

Did you want to lock it completely for every opened window? (Say, Word, notepad, etc.)