Just an idea that may have no merit: You said that in device manager there were no video drivers installed to start with. It may be worth looking in Add/Remove software to see it your buddy installed some incorrect drivers that were not properly detected but are causeing a conflict anyway. You may also want to try DriverCleaner
http://www.drivercleaner.net/ ... follow instructions and reinstall your nVidia drivers. Other options include checking to make certain all connections are good including reseating the videocard itself.