Multiple File open alert

In Windows XP, when you try to open a lot of files at once, a warning
pops up asking if you're sure you want to open that many files. There
are Yes/No buttons and a checkbox for "do not display this message
again" Once you check that box, how do you get the message to display
again.

Yes I accidentally checked that box and I want to restore the warning.

Thanks

crn

.