Have XP Pro, SP2 on all machines. About half of them are running dual monitors. Works great, just plug the second one in via a USB port and go to Control Panel/ Display/ Settings and set up which one you want to be No. 1 and 2. But have a new monitor to plug into a system and it won't work. I've plugged this monitor into another system and it works fine. I get power and I get a test pattern of a sort on the monitor itself when it's plugged into the correct computer. I've replaced the USB cable just in case. And I get a little prompt that tells me it's found new USB port. The problem is, when I go to Control Panel/Display/Settings the dual monitor icons and options are not there. And I know it is there whether you have a dual monitor or not, it does not depend on whether or not you've added this hardware. So where is it? How do I get it? This is generally one of the easiest things to do......