ADE “Not Responding”

I primarily use ADE as the default app for opening epubs upon their initial export from InDesign, in order to quickly check that they are exporting correctly. It has always functioned in this capacity with no problems. As of last week it will no longer open epubs: neither newly created epubs, nor previously existing epubs that were opened by ADE with no problems in the past. Instead, it just prompts “Not Responding” and I have to kill the process from the Task Manager to stop it.

ADE 4.5.1.  I have uninstalled ADE ad re-installed a fresh version—no help.

Windows 10.  Most recent updates.

Am I missing something basic?

Thank you.