Gears of War is defective by design
Epic Games's Gears of War title apparently includes a cut-off date, enforced via DRM. Ars Technica is reporting that the game ceased to function for everyone who bought it on January 28, 2009.
While it's not rare for games to ship with bugs every now and again, it's pretty shocking when one ships with an issue that causes the title to stop working for everyone who paid.