Company computer updated to windows ten, unwanted and completely bricked the cash register while it was installing

I work at a family company. It's a bait shop down on Cape May here in south Jersey. For the past two years we've had windows 8 which, while not perfect for me to use (as a windows 7 user), still suited its purpose. It worked fast and efficiently and when the day was done, we backed up our finances and headed home.

However, recently, about a week or two ago, the computer shut down in the middle of work hours. My mother tried frantically to get it back up and when it did come back online, it was updating to Windows 10. It was down for quite awhile too. Luckily it was a slow day, but my father was not happy. A few years ago, our old computer (the reason we got the new one with windows 8) was randomly corrupted and a lot of data was lost. So my mother and my father were both very vigilant when it came to pop ups and computer errors.

My father is no idiot with computers. He knows somewhat about Microsoft's malicious use of pop ups to upgrade, but my mother said nothing ever came up. So now all three of us are scratching our heads

Now with windows 10, our applications are notably slower and the desktop icons for google chrome for our fish registry websites no longer work.

I need to know what happened, why, and how can I fix this?