I was working on a simple project with a single model, a backdrop and lamps, and suddenly, Blender became really, really slow. I tried starting a new project, restarting the computer, even reinstalling Blender, but nothing seems to help. What could have happened and what can I do to resolve it?
I recently ran into the same problem. I found this similar one Blender 2.78 with Windows 10 lags when interacting with the UI, which seems to indicate a problem with Windows 10, which I was running. But I found that the solution was to right click on the blender shortcut>Run with Graphics Processor>Integrated Graphics. Mine immediately went back to running fast when I did this.