Hibernating laptop randomly wakes up and stays on when lid is closed

From the How-To-Geek article on troubleshooting computers that wake up when they shouldn't:

First, to find out what woke up your computer today, use the following command in a Command Prompt:

powercfg -lastwake

To see all the devices that can wake your computer, use the command:

powercfg -devicequery wake_armed

To get a better picture of what's happening when your computer is woken up, use the Event Viewer. Open the Windows System Log, choose Filter Current Log, and in Event Source find the Power-Troubleshooter option. This is a great way to learn when your computer has been awakened, and which scheduled tasks may have triggered it.