WP asks reinstall every time I modify something in dashboard

Hello,

I got this problem since I tried to modify a css through FTP (I don’t have CPanel from host).
After I modified the css I uploaded it again back to the server. After that, the message appeared that I have to reinstall wordpress.
I checked to see if wp-config.php is ok and it is. Everything is fine.
After a while the site works again like nothing happened.
When I try to do anything in the dashboard and save it, after that the install error appears again.

What is going on and how can I fix this ?

Thank you !