When you use Remote Desktop Connection (RDP) to connect to a computer running Windows 8 you lose the shutdown/restart option to prevent people from accidentally shutting down their computer when they’re not sitting in front of it in case they need it powered back on. You only get the option which allows you to “Disconnect”.

Go to the desktop and press Alt+F4.

You will then be presented with options to:
Sign Out

Choose Restart and then it should restart, give it 5 minutes and you should be able to reconnect.