Using a Lenovo T400 (XP operating system) with external LCD flat screen monitor. Recently the display started 'flopping' back and forth between the two displays - the external and laptop. Have done much trouble shooting, including new cable between laptop and monitor and trying another, tried two different external monitors - both have same issue, support replaced PC thinking it was the port, support replaced hard drive, loaded all drivers repeatedly etc etc. The problem is mostly contstant but I can go hours sometimes without the issue. If I bring up Intel graphics properties while it is having this issue you can see status change between the two monitors. And, at times, it will say I am on external monitor when I am only on laptop with no external connected. PC seems unable to determine what monitor is in use and will not hold display to external. Looking for any suggestions.