Dynamics NAV Server not installed on already present NAVDEMO SQL Instance.

We have Installed SQL Server with instance name as NAVDEMO. After that we installed NAV 2013 R2 and chose the option as Install Demo. NAV 2013 R2 got installed and did not installed SQL Server Express as expected, but NAV installation did not installed NAV Server or the service for using RTC. I am getting an error in the NAV 2013 R2 Admin console that the dynamic NAV server is not installed on this computer. If I check the service there is no service for dynamics NAV. Now how do I install the dynamics nav server for RTC.

Did you try to run Microsoft Dynamics NAV Service installer from CD_DVD\2013 R2\ServiceTier