https://answers.yahoo.com/question/index?qid=20080810132332AAr5nSv
This may return an error message "The requested operation requires elevation". What this is trying to say is that you have to be Administrator to run it. This turns out to be easy to solve; when starting the command window, right click on the launch icon and select "Run as Administrator". If you have the admin password or are a Power User this will work easily:
http://answers.microsoft.com/en-us/windows/forum/windows_7-performance/error-the-requested-operation-requires-elevation/cdd97f8c-7f58-e011-8dfc-68b599b31bf5
