If you've just upgraded your Windows 8 (non RT) device to Windows 8.1 and suddenly upon reboot you're facing a quietly humming computer with a black screen of nothingness....don't panic. You've probably just got Master Boot Record issues. This can be a fairly easy fix, particularly if you've already created a Windows 8.1 Recovery disk. If not, you'll need to use your bootable install media for Windows 8.1 or find a working Windows 8.1 device and create a recovery disk.