First sign in to your online account here: http://home.mcafee.com/Default.aspx?culture=EN-GB (top right) and go to your subscription.,
Click on subscriptions and deactivate the license in use for that machine.
The page looks a little like this: (Click to enlarge...this is a pic of my own account so product names may vary)
When you click Subscription it should open up to look something like this (I've named my entries so I know what they apply to but usually by default they bear the name you've given the computer at Windows setup.
Once that's done uninstall all McAfee from your machine, then run the MCPR cleanup tool available via useful links at the top of this page and reboot immediately it tells you to.
Go back to that account page above and download your product from there, don't use a CD or other means.
That should hopefully fix things.