Tried to fix start menu issue, lost profile, had to use system restore

There are countless posts on here about fixing the problem of the Win10 start menu disappearing (that is, left-click the start button and nothing happens).

My wife got her ASUS laptop in early September, and some time - a month or two maybe; it's her computer, but it was me who noticed - later, the start menu functionality disappeared.

This bothered me a lot more than it bothered her, but I'm a big believer that small visible problems can be a sign of bigger lurking ones. So I finally got around to attempting to fix it.

It seems like almost universally, the first recommended fix is to open a powershell window and then do the sfc /scannow. So I did that, and it found some corrupt/missing files and fixed them. But that didn't fix the problem.

Other common steps I've read - registry edits, there is a batch file touted in these forums, much more - seemed to get far less than unanimous endorsement and I didn't want to make things worse. So my next step was to pick "personalize", click "start" on the left menu, then click "Start" from the available choices. From there I tried to toggle "Use Start full screen" on and off, but Win10 never would "remember" the change. It would be "on" and then revert to "off" with no intervention from me.

After that I rebooted the computer, logged in - and instead of just bringing me to the normal desktop, 2+ minutes went by with the spinning dots and "Preparing Windows" displayed.

When the login completed, it was my wife's user account, and the start button/menu worked (good!).

BUT... it was like she'd never been on the computer before, ever.

Desktop background picture was different.

Firefox was no longer her default browser, and none of her profile information - bookmarks, passwords, browsing history - had been saved.

Her Documents folder existed, intact, but the system pointer to "My Documents" pointed elsewhere (to something, an empty folder, buried several levels deep in Temp).

The home network printer was visible, but not accessible. I had to delete it and manually re-add it.

And so on.

And the account WAS her account. Same user name, same password, and looking through the App Data folders, they were created on 9/3, the day the computer was configured. But nothing was the same, and much was lost.

Desperate, I opted to do a system restore, back about 10 days. Upon completion, we got a message that the restore failed because - well, I forget, but it had something to do with a persistent file that the restore was unable to eliminate or overwrite or something.

However, then everything was back to as it had been before I started. All the good/expected things about the computer configuration, but the start button/menu no longer worked again.

So:

1. Even though it gets asked a lot, how do I restore Start button/menu (without the disastrous consequences I encountered)?
2. What the heck happened, so that a seemingly superficial/benign "poke" at personalizing and playing with the "start full screen" setting, caused her user profile to complete reset on reboot? By the way, the computer is scanned daily by AVG and is clean, and I ran a Malwarebytes scan before playing with anything, and that too found zero instances of malware.

I solved the same issue you had by doing an in place upgrade of Windows 10. Solved the problem and everything user account wise remained the same.

Thank you Dalchina for the reply, and the instructions.

I'll push this off to the weekend, since it's my wife's laptop, and both she and I are occupied in the evening during the week.

Sadly, I regularly image my own C drive, although I'm the "safest computing" practitioner in our house. The more "rogue-managed" computers, more likely to go off into the weeds, I don't. Very bad on my part, I admit. I've used Drive Image on my own computer all these years and it's worked great. The Macrium free product sounds wonderful though; I will have to check it out.