Daryl is running Windows 8.1, but after a so-called critical update, he gets a black screen. Leo says that sometimes an update can break something, and it sounds like it may be an incompatible video driver. First thing to do is to boot into Safe Mode. Then, if his screen comes up, that indicates a driver issue. Daryl should go to the video card manufacturer's website and download the latest video driver. There's some other suggestions at answers.microsoft.com here.
Leo also suggests getting his install disk and running the "Repair" routine. That'll fix any problems and get him back up.