Michael
There are several reasons for boxwoods to show yellow/dying leaves.

A common cause in the late winter/early spring is winter burn due to cold winter winds, ice, and cold. You can minimize winter damage by erecting a wind protection around the bush in late fall, e.g., wrapping in burlap. A thick layer of mulch around boxwoods can also keep the root warmer.

Boxwoods are also susceptible to a growing number of pests. If you suspect insect damage, you should treat immediately. A relatively new and serious problem is the fungal disease called boxwood blight. The links below give some information.
https://bygl.osu.edu/node/1359
https://bygl.osu.edu/index.php/node/2198

Salt used for sidewalks and roadways can also cause damage to boxwoods. In this case, parts of the boxwood closest to walking surfaces should show the worst damage.

Root rot is another possibility. Boxwoods are very sensitive to excess amounts of water. The roots can be damaged when exposed to too much water, and the bush cannot absorb nutrients from the soil. The best way to solve this problem is to add a layer of sand or peat moss to the ground. Note, boxwoods should be planted in a well-drained area in light, fertile soil. Avoid depressions where water can collect.

Another possibility is damage from dog urine. Yellowed areas that are circular and relatively low to the ground can indicate this issue.

I hope this information is helpful.
Roxanne

Roxanne, thanks for your help! 

Michael
I would give it two more weeks.

Then, if you can see green emerging, I would suggest you cut back to the green. In case it is a disease, I suggest you dunk your pruners in a 1:9 chlorox:water mix after every cut.

If you see signs of insect damage, you should treat for that as well.  

Water sparingly when only when dry and water at the base, not the leaves.  Do not fertilize until you see new growth again and I suggest you only use half-strength fertilizer.

Roxanne