I've run Qt on this system for a few weeks with no problem at all. But with no apparent change to the system at all, the Welcome component of Qt Creator now gives this error message:

Welcome Mode Load Error

Failed to create OpenGL context for format QSurfaceFormat(version 2.0, options QFlags(), depthBufferSize 24, redBufferSize -1, greenBufferSize -1, blueBufferSize -1, alphaBufferSize -1, stencilBufferSize 8, samples -1, swapBehavior 2, swapInterval 1, profile 0) .

This is most likely caused by not having the necessary graphics drivers installed.

Install a driver providing OpenGL 2.0 or higher, or, if this is not possible, make sure ANGLE Open GL ES 2.0 emulation libraries (libEGL.dll, libGLESv2.dll and d3dcompiler_*.dll) are availble in the application executable's directory or in a location listed in PATH

I uninstalled and reinstalled Qt, but that did not help. The information I found online of people with similar problems was related to VM, but this machine is just a regular Windows 8 PC.