Some users are complaining on Microsoft's support forums that their computers cannot be turned off or rebooted using the built-in power options.The only way to shut down the laptop is to manually press the power button, one user explained, as the available options do absolutely nothing.
“After installing Windows 8.1 Preview, my computer will no longer shut down or restart. I have to manually power down (10 seconds on the power button). All drivers are up to date, and Window Update does not indicate any pending updates,” he explained.
Microsoft rolled out the first Windows 8.1 Preview updates this week, so make sure you get all patches if you're encountering similar problems. A new batch of fixes is expected anytime soon, so keep an eye on Windows Update to install them as soon as possible.