I cannot get SQL Server 2012 to install the database engine
SQL server 2012 installation is not supported through terminal services.  It causes a lot of strange problems, and I experienced this same issue.  

Microsoft states this in their prerequisites:

Link is http://msdn.microsoft.com/en-us/library/ms143506.aspx 

This document states:

The installation of SQL Server 2012 fails if you launch the setup through Terminal Services Client. Launching SQL Server Setup through Terminal Services Client is not supported.