How to help neck pain from computer?

Physical therapy. Constant neck flexion from repetitive computer work results in chronic neck extensor muscle fatigue. Strengthening and postural reeducation will alleviate this chronic condition.
Lots. First, make sure the screen is not too high or low as you will likely have more pain if you hold your neck flexed or extended. Second, don't sit for hours without taking a break to walk around and stretch your neck and shoulders. Break at least once an hour. Third, get regular exercise - keep joints loose and muscles strong.