The screen may flash when you connect an external display or when you use an external display on a Windows Vista-based portable computer

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.

This problem occurs because of electromagnetic noise on the VGA cable.

In Windows Vista, the Transient Multimon Manager (TMM) detects the connection and the disconnection of external displays that use an analog connector. The TMM polls the analog connector one time per second. However, because of electromagnetic noise on the cable, the TMM may incorrectly detect that the connected display is frequently being connected and disconnected.

Correct the VGA cable problem

Ask the system administrator to examine the VGA cable. If there is a problem with the cable, use a cable that is shorter or that is of better quality.

Advanced Troubleshooting

Set the TMM not to periodically detect the analog connectors

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

Set the TMM not to periodically detect the analog connectors. To do this, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TMM
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type PollingInterval to name the new value, and then press ENTER.
5. Double-click PollingInterval, type ffffffff in the Value data box, and then click OK.
6. Exit Registry Editor, and then restart the computer.

Note Even if you set the TMM not to periodically detect the analog connectors, an independent hardware vendor (IHV) graphics driver may detect the connection. Therefore, this problem may still occur. If the problem still occurs, contact the manufacturer of the portable computer or the vendor of the graphics driver.