Please help. I try to download a game, and when completed, file either won't open. Or opens and says I've only got 2 minutes left on demo. What am I doing wrong?

You need to be careful downlding programs such as games. Usually the largest are the best to aim for. Those that are disk images are probably best. But that's part of the mystery when downlding such ... you never know what you're getting ... yes sometimes people share demos, etc.