By default, after waking Windows Vista from sleep state it displays a screen where you have to pick the user whose session you want to resume. The screen is displayed even if that user doesn’t have any password set. To enable automatic session resuming, you need to modify the power plan settings.
- In the Control Panel select System and Maintenance → Power Options.
- Click the Change plan settings link under the name of the plan you are using.
- On the new screen, click the Change advanced power settings link.
- In the window which has just appeared on the screen, click the Change settings that are currently unavailable link.
- Set Additional settings → Require a password on wakeup to No.
- Repeat the operation for every power plan you use.