Windows 8.1 Preview was officially retired yesterday, so all machines that are still running it right now are automatically restarting every two hours.
Microsoft wants all users to move to the full version of Windows 8.1, as it provides several performance improvements over the preview build, as well as enhanced functionality that makes it more helpful for users worldwide.
Windows 8.1 Preview was launched in June 2013 at the BUILD developer conference and was supposed to provide us with a short glimpse into the feature line of the first update for Windows 8.
The full version of the operating system, on the other hand, arrived in October last year and brought quite a lot of improvements, including the highly-anticipated Start button that was removed in Windows 8.
Windows 8.1 Preview machines cannot be updated to the full Windows 8.1 version without losing apps and settings, so a clean installation would be a pretty good idea in this case.