Hi, I'd like to inform you that by default the power button in Windows Vista is sleep. We can edit power option to change it to shut down:
1. Click Start, go to Control Panel.
2. Double click on Power Options.
3. Go to "Change plan settings", "Change advanced power settings".
4. Go to Power Buttons and lid -> Power button action -> Setting: Shut down.
Let's check if this resolves the issue.
Sean Zhu - MSFT