On a Windows Vista-based portable computer, you use a VGA cable to connect an external display. For example, you connect a monitor, a projector, or a television to the portable computer. The screen may flash when you connect the external display or when you use the external display. This problem occurs if one of the following conditions is true:

• The VGA cable is long.
• Multiple VGA cables are connected to one another.
• The VGA cable does not have effective electromagnetic shielding.