You installed the Server Core, which does not have a GUI.  You'll need to reinstall and select the GUI option (unless you know how to configure and manage your server from the command line using PowerShell and/or remote management tools (MMC)).
I installed Windows sever 2012 R2 on my Dell 2950 the install seemed to go fine now I get the "press Ctrl +Alt+Delete to sign in" prompt the next screen asked me for my Admin password. When I enter my password i get a dos prompt with a blinking screen, accros the top reads C;\ Windows\system32\cmd.exe what do I enter at the prompt to continue. Thank You 
Windows Sever 2012 R2 installation