Problem Registering/Installing

[London Calling]

I've recently purchased DEFCON. On trying to install it my computer just reads the disk and seems to make some attempt to autorun it but can't. I'm not having any problems running the demo so I think it coud just be a bad disk. However, I've still got the authentication keycode to upgrade the demo to the full version but can't find the 'Authentication' option in the 'Options' in the main menu. Any clues anyone?

ACER Aspire 3020 running XP
AMD Sempron 1.8
512Mb RAM
ATI Mobility Radeon X700

[ynbniar]

Options
Authentication

Enter your code.
(you might have to click somewhere on the code entry boxes)