Keep Windows 10 Preview Up to Date or Face a Dead PC
 

Microsoft has a strange way of keeping you up to date if you are running Windows 10 Preview; your PC won't boot up. A not too subtle hint that the build that you are running isn't in the best interest of Microsoft and you have to upgrade to the later 2015 Builds, which will also stop booting on October 15th when the Preview program officially ends. The first three builds of Windows 10 Technical Preview—9841, 9860 and 9879, all released in 2014—will refuse to boot at the end of April, according to a message posted by a Microsoft support engineer on the company's discussion forum.

http://www.hardocp.com/news/2015/04/..._face_dead_pc/