Non Operational

My Acer Laptop has Windows 8.1 façtory I installed. When the "free trial" for WIndows 10 was available, I decided to give it a try. I did not like it due to the fact I could NOT download Google Play Store and my banks Apps. Banking On-Line, this is how Is pay my bills. With Windows 10 I could not bank on-line. Needless to saý I removed WIñdows 10.
For the past four months I have been using my sisters ASUS Laptop merely for the use of Office Word a d Excel (she was able to get one of the last "lifetime" Office offers. She installed it and since it only allows one device to be installed on, I have been using the laptop.
The other day I needed something that I knew I had on my laptop. When I turned it on everything started as usual then, this error code came up. I was locked out and unless I had a Windows 8.1 disc to re-install I basically have dead laptop., a "sail" item, a boat anchor...
What can I do to get this back in operational mode and will I lose all my stored files, photos and music ? I'm not teçh savey, however if explained in simple layman's lingo, I can follow along..

Hoping for a positive outcome here.
Sandy Crabtree