Empty page instead of Nextcloud

Nextcloud version
Operating system and version Ubuntu 16.04.4 LTS:
Apache or nginx version Apache/2.4.18 (Ubuntu):
PHP version PHP 7.0.30-0ubuntu0.16.04.1 (cli) ( NTS ):

Is this the first time you’ve seen this error? Y

The output of your config.php file in /path/to/nextcloud:

$CONFIG = array (
  'instanceid' => 'xxx',
  'passwordsalt' => 'xxx',
  'secret' => 'xxx',
  'trusted_domains' =>
  array (
    0 => '',
    1 => 'xx',
  'datadirectory' => '/var/www/nextcloud/data',
  'overwrite.cli.url' => '',
  'htaccess.RewriteBase' => '/',
  'dbtype' => 'mysql',
  'version' => '',
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'nextclouduser',
  'dbpassword' => 'xx',
  'installed' => true,
  'skeletondirectory' => '',
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
  'default_language' => 'ru_RU',

The output of your Apache log /var/log/apache2/error.log

My nextcloud worked well until my proxmox is felled ill.
I moved virtual disk of nextcloud to another proxmox disk.
After I did it - Nextcloud doesn’t starts (but I can connect it via ssh).
When I enter IP in browser I see empty page.

Where I can find the solution, what should I do?

Looks like it is “Failed to connect to the database”. Check your DB is up and running (and accessible to Nextcloud user/instance) and also check that you have space left on your hard drive, other errors are related to it.