To access the Run box in Windows Server 2012, press 'Windows+R'. The PowerShell console can also run any kind of Windows command, so you don't need to open the old command prompt to run DOS-style commands. You can open PowerShell using the blue icon on the desktop taskbar or by typing 'PowerShell' on the Start screen and selecting 'PowerShell' from the search results.
Alternatively, to open a standard command prompt, type 'cmd' on the Start screen and select 'Command Prompt' from the search results, or press 'Windows+X', where you can run the command prompt with or without admin credentials.
