SharePoint 2013 Site Settings URL

Working on migrating our SharePoint from 2010 to 2013. I did the upgrade of the content database but then I couldn't get to the site settings because of a file not found exception. What I found I could do is go directly to the settings URL "http://xxx/_layouts/15/settings.aspx". Once there I went to "Master page" under "Look and Feel" changed the Site Master Page and System Master Page to one of the standard pages.