Is it the 2011 demo? 2011 has some compatibility issues with previous versions of max. Just completely uninstall all previous versions of max (afterburner included) and try again. Also, if you check the website it says "Microsoft Windows XP Professional x64 (SP2 or higher)". Make sure it's up to date, also update your graphics drivers and make sure you're installing the right version (32 or 64 bit).
Try running a scan aswell, if it is a max problem it might be to do with antipiracy, make sure you're actually installing the demo.
Check that your computer meets the requirements, it will error out if it doesn't.