'Access is denied.' on windows 7

Hello, I try to install ruby 1.9.2p0 with the rubyinstaller, I’m
following a video, and when I install and try to access by prompt, the
follow message appears…

Microsoft Windows [Version 6.1.7600]
Copyright © 2009 Microsoft Corporation. All rights reserved.

C:\Users\Felipe>ruby -v
Access is denied.

Thanks.