No puedo acceder a la pagina administrador pongo usuario y contraseña y al hacer click en acceder me vota una pagina en blanco

Buen día, tengo dos problemas, uno es al acceder como usuario me sale una pagina en blanco y dos no se muestran los pdf, por favor si alguien me puede ayudar?
[12-Jun-2019 00:49:04 UTC] ojs2 has produced an error
Message: WARNING: session_start(): Cannot send session cookie - headers already sent by (output started at /home/revistasuancvedu/public_html/classes/core/PageRouter.inc.php:67)
In file: /home/revistasuancvedu/public_html/lib/pkp/classes/session/SessionManager.inc.php
At line: 60
Stacktrace:
Server info:
OS: Linux
PHP Version: 5.6.40
Apache Version: N/A
DB Driver: mysql
DB server version: 5.7.26
[12-Jun-2019 00:49:04 UTC] ojs2 has produced an error
Message: WARNING: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/revistasuancvedu/public_html/classes/core/PageRouter.inc.php:67)
In file: /home/revistasuancvedu/public_html/lib/pkp/classes/session/SessionManager.inc.php
At line: 60
Stacktrace:
Server info:
OS: Linux
PHP Version: 5.6.40
Apache Version: N/A
DB Driver: mysql
DB server version: 5.7.26
[12-Jun-2019 00:49:04 UTC] ojs2 has produced an error
Message: WARNING: session_regenerate_id(): Cannot regenerate session id - headers already sent
In file: /home/revistasuancvedu/public_html/lib/pkp/classes/session/SessionManager.inc.php
At line: 250
Stacktrace:
Server info:
OS: Linux
PHP Version: 5.6.40
Apache Version: N/A
DB Driver: mysql
DB server version: 5.7.26
[12-Jun-2019 00:49:04 UTC] ojs2 has produced an error
Message: WARNING: Cannot modify header information - headers already sent by (output started at /home/revistasuancvedu/public_html/classes/core/PageRouter.inc.php:67)
In file: /home/revistasuancvedu/public_html/lib/pkp/classes/core/PKPRequest.inc.php
At line: 87
Stacktrace:
Server info:
OS: Linux
PHP Version: 5.6.40
Apache Version: N/A
DB Driver: mysql
DB server version: 5.7.26