Error establishing a database connection

Hello…
Whenever i try to log into my site to make any changes or whenever someone else tries to logs into my site, it doesnt work.
I cant go into the WP Admin panel to add new sites, i cant access the site whatsoever. i changed nothing, half an hour ago it was working perfectly fine, i installed no new plugins, no updates, i wasn’t even at the computer but now i can’t login.
My site is still online since i can browse the articles that are online and i can read the articles (www.thenewlight.eu) but login doesnt work. (https://thenewlight.eu/wp-login.php)

I could really use some help, i have no clue what’s going on.