Click Start menu(Win Menu)
Click Run. If you are using Windows XP you'll see the Run icon in your start menu itself. If you are using Windows 7 type run on your start menu search and then you'll see the Run Icon.(Instead of Step 1 & 2 you can press Win Key + R to get the Run Command Wizard)
In the Run Command Wizard type "shutdown -s -t time_in_seconds" without the quotes .Ex : shutdown -s -t 600, this will shutdown your computer after 10 Minutes.
Click OK
after the -t you have to give the time in seconds. Suppose your want to turn off your computer after 1 Hour then use the Calculator to find the seconds, 1*60*60 will give you the result 3600. And then your command is shutdown -s -t 3600.{WWW.AIRTELTRICKZ.MOBIE.IN}