It is a real story and is one of my scariest tech experiences.
Most users think that IT experts like us know how to fix all computer problems. This belief is true depends on two factors.
Details of the story are in the question below.
Technically, it was an easy task as initially, I assumed Windows 10 is much better to handle as you can do a reset and add the email account of the new user and enter all required network credentials to make the computer as new. Obviously, my initial assumption about resetting a Windows 10 PC as an easy task was incorrect as a reset did not work and time was running out so I set up a new user profile to solve the problem.
Everything was fine except that on every restart, a prompt appeared to ask what app I want to open for an unknown file.
If time was sufficient, I could do a clean install of Windows 10 to get rid of the problem. However, it was unlikely that I could tell the new user, who is the Executive Director of our company that it was a minor problem that I could fix it later. It was a Friday evening and I HAD to finish the task as a delay would ruin my career.
At that time, the fastest method to solve the problem was to ask a question on Experts Exchange as I was pretty sure that I would get a solution soon.
No need to repair windows. A repair will not get rid of that item.
Download autoruns.exe and use it to deactivate it.
Autoruns by Microsoft is a tool to show and stop what programs are configured to run during system bootup or login or start various built-in Windows applications like Internet Explorer, Explorer and media players. It is a complete list showing all auto-start processes and services from all users in Windows OS.
The Lesson learnt
IT experts are just HUMAN and there are times we need the help from our peers. Being a member of Experts Exchange DOES HELP me a lot when I have a problem and at the same time, I can learn more by helping other members to solve their problems.