When installing Exchange 2013 in an environment with Exchange 2010, there is no link or application for Exchange Admin Center. Open a browser and type https://<Servername>/ecp/?ExchClientVer=15, this will give you direct access to the Exchange 2013 server, not on the Exchange 2010 server where the mailbox may reside.
Exchange Admin Center redirects to OWA
When installing Exchange 2013 in an environment with Exchange 2010, there is no link or application for Exchange Admin Center. Open a browser and type https://<Servername>/ecp/?ExchClientVer=15, this will give you direct access to the Exchange 2013 server, not on the Exchange 2010 server where the mailbox may reside.