By default, when you are remote desktop-ed into a machine, the start menu does not show an option to shutdown or restart. These options are not even shown in the Task manager. A quick google search turned up a reply from Mark L. Ferguson, Moderator on Social.Answers.Microsoft.com.
here’s the skinny:
press the windows key + r
Type in shutdown -r -t 0 <- That’s a Zero
the ‘-r’ parameter tells shutdown.exe to ‘restart’ and the ‘-t 0′ tells the application to show zero pop up warnings