Windows Vista is automatically set to a power setting called the "Balanced" power plan. This power plan setting seems to be fine for desktop computers and laptops that are plugged in. But laptops working on battery power may require an adjustment of this setting. Here's how:

1. Go to Start>> Control Panel>> Power Option icon.
2. From here, you can select a different "Power Plan" or you can change the settings of the selected power plan manually.
3. To adjust the selected setting, click the "Change Plan Settings" link under the "Balanced" entry.
4. Adjust the settings to fit your systems needs or you can dive a little deeper by clicking the "Change advanced power settings" link.
5. When you are finished, click the "Save changes" button at the bottom of the window.