I have a MacBook with MS Vista on it. Until this past weekend I was able to run my computer in clamshell mode with no problem on Vista, then this weekend Vista stopped recognizing my external monitor. It shows 2 monitors with the external one grayed out under the display control panel. When I try to make the external monitor my primary monitor, nothing happens. I am really confused what happened here. Should I just uninstall Vista and go back to XP. I need Windows to use GIS software (I am an urban planning student) and the smaller screen on the Macbook makes it hard to work with the software. Thank you all for all of your help!