|Depending on the version and how you bought it you may be able to install it.|
How did you get the program? Is it a file or a cd or what?
You may wish to consider also other free security suites if you can't get this working. MS offers security essentials and there are other free av like clam and anti malware spyware apps out there.
A Pit Bull is like a gun you can pet. And there is no safety on it.