This is resolved! I found a problem with Plugins and in my .htacess – file.
If after Multisite-network install no Theme is shown, then add disable all Plugins in the Networkadmin-Panel and add the following lines in your .htacess file:
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
# add a trailing slash to /wp-admin
RewriteRule ^wp-admin$ wp-admin/ [R=301,L]
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule ^(wp-(content|admin|includes).*) $1 [L]
RewriteRule ^(.*\.php)$ wp/$1 [L]
RewriteRule . index.php [L]