If you have downloaded a demo or purchased a game and it does not launch, try the following steps:

Demo - Use the remove button to remove the demo and then download the demo again by going to the product and clicking on "download demo".

Purchased game - If you purchased a game and it does not run, try to reinstall it. The reinstall button is next to the game. This will download a fresh copy of the game and reinstall the game.

If this does not fix your problem, then it is possible that the game is not compatible with your Mac or Mac OS X version.