Hello, and welcome to the new Help section. Since you've got this far there's no need to go into issues about discs not working at all, but if you're having problems with a disc other than this one then the Website button will take you to the Disc Support Forum, which deals with all known issues and is kept up-to-date with any problems we find people have been having. Also there is a link to e-mail me, the Disc Editor, if the problem your having isn't dealt with anywhere there.
If you're having trouble with a specific demo, the chances are it's not a fault with the disc. Faulty discs are very rare to begin with, and when they do go wrong they almost always go completely wrong - the interface wouldn't start up and the disc wouldn't be browsable in Explorer. If you are having trouble installing a specific demo, take the disc out and check it isn't dirty or scratched. Even if it doesn't appear to be, clean it with a clean dry cloth to be sure.
You should also check that you have a lot of disc space free. At the moment few demos require more than 1GB free, excluding time-limited trials of full games. If you have plenty free, try opening the Content folder on the disc in Explorer, finding the file that corresponds to the game you're trying and dragging it to your desktop. Once it's finished copying, double-click the file on your desktop, and it'll run the installer from there. If that doesn't solve it, check the Disc Support Forum for any known problems with that issue, and if there's nothing relevant there then send it back to us. See Returning A Faulty Disc.