Artuu
Ok, now follow the steps that I listed above. Open ssh and browse to your webroot. Once there, type
nano config.php
Once that loads, find the line that says
debug=false
and change it to
debug=true
Once you are done that, browse to your website again, and see what the error is. Post it here
I am just taking a guess, but I think that your vendor directory isn't properly chmodded. Some of the folders inside the directory need to be chmodded.