Are you talking about the home screens, or elsewhere? The home screens don't rotate unless in the car dock (or using an app like Ultimate Rotation Control).
Drop it. My phone wouldn't auto-rotate anymore a few weeks ago, I reflashed stock, calibrated the gyroscope, and a couple more "fixes" that didn't work. Then I read somewhere to drop it on its back from about 5-6" on a hard wood floor. Bingo, its auto-rotating.