This problem of my desktop flickering or refreshing about every 2 seconds started occurring today on my desktop machine after a reboot. Microsoft has a page describing the issue here: https://support.microsoft.com/en-nz/help/12374/windows-10-troubleshoot-screen-flickering
The computer is almost completely unusable while the problem is occurring; no apps can be opened, and the Start menu won't open. Right clicking the system tray opens a context menu sometimes but closes again almost instantly when the screen flickers next.
According to the diagnosis process provided in the above link, in my case the problem wasn't caused by display drivers because I was able to open the Task Manager with ctrl-alt-del and the Task Manager window didn't flicker like the rest of the desktop did.
Apparently this means an application is incompatible with Windows 10. This is a bit weird really because I've been using Windows 10 for months with no problem, and haven't installed any new apps recently.
Microsoft suggests removing 3 particular apps that are incompatible, however that wasn't possible as I couldn't get into the Settings window to uninstall anything, let alone check which applications were even installed.