>I have a modal form that on one computer the "X" close button is visible but on my other two computers the "X" close button is not visible.
That can occur when the focus gets off the active modal, it's kind of a bug, but it also usually means your design is a little confused, I've been there myself :)
The Anonymous Bureaucrat,
and frankly, quite content not to be
a member of either major US political party.