I recently bought Grand Ages Rome and intend on buying Dawn of Discovery. I played a little 1701 AD recently as well.

I usually buy the cds but if I find a digital download of a game I like I will do that as well.

Sup Com for quicker action, Sins if you have all day.

Firaxis, just because I am a fan of the railroad series.

This sounds copy protection related. You can take the dvd out and make sure its under side is clean (there are no spots or anything). If you have a different dvd drive you can also try that.