But what do you do when you can't right-click, you are running in "core" mode, or the GUI isn't running properly? Well, PowerShell to the rescue...
If you can open PowerShell, type:
Start-Process cmd -Verb RunAs
If you can't, but can open a (none-admin) command prompt, type:
Powershell -Command "Start-Process cmd -Verb RunAs"
Powershell -Command "Start-Process cmd -Verb RunAs"
You may get a UAC prompt, but essentially this will open an elevated command prompt.
Note: This has been tested in Windows Server 2008, 2012 and 2016.