You install a Windows Vista Service Pack on a computer that uses multiple monitors. Then, the custom display settings may revert to default display settings. The custom display settings that revert may include the following settings:
Default monitor choice setting
Monitor position setting in a multi-monitor configuration
Monitor display size setting
Monitor update setting (monitor refresh rate) and video adapter update setting (video adapter refresh rate)
This issue occurs because certain device drivers are reinstalled to correctly service the underlying components during an installation of a Windows Vista service pack. Therefore, certain customized display settings may be reset to their operational default settings.
To resolve this issue, reset the custom display settings on the computer. To do this, follow these steps:
Click Start, type personalization in the Start Search box, and then click Personalization in the Programs list.
Under Personalize appearance and sounds, click Display Settings.
Reset the custom display settings that you want, and then click OK.