Uninstall node-sass: npm uninstall node-sass
Delete package-lock.json, and clean the cache: npm cache clean --force, then do npm update, npm install, npm update. then again try to install node sass: npm install node-sass.
If this doesn't work, Try to rebuild node-sass:
npm rebuild node-sass
If that too doesn't work then i suggest to delete package-lock.json, node-modules and npm cache folder and do npm install , to install all your dependencies again. make sure you have a package.json file with all your dependencies listed.
The package-lock.json file has some issues(it doesn't update when package.json changes) as mentioned here:https://github.com/npm/npm/issues/16866
"Touching package.json by hand may make your package.json to be incompatible with package-lock.json". do npm update to update the package-lock.json file.
to completely disable package-lock creation:
npm config set package-lock false
