Joystick will not calibrate on Y-axis

I am unable to get my joystick to calibrate properly on the Y-axis. I originally thought is was the joystick, since it was rather old. However, I recently purchased a new one (a Gravis BlackHawk), and am having the same problem. If I let the joystick center it behaves as though I had it pushed full forward. Any ideas why…and how to fix it?