Many fertilizers contain mineral salts that can dry out the soil, making the lawn wither. This condition is called fertilizer burn and can be solved by filtering out some of the excess salt in the soil. The best action to take is to apply 10 lbs gypsum per 100 square feet of grass and water everyday process.
Since you might have over fertilized, or did not get any water on the lawn soon after fertilizing, you might have killed the grass in those areas. You'll have to rake out that grass, rough up the soil up a bit, and reseed.
Those brown patches are the result of excess fertilizer in those spots. Thorough watering of those spots will bring the grass back in about 3 to 6 weeks. If you were to reseed those spots, it would take almost as much time for the seed to germinate, so just water and be careful the next time you fertilize.
You over fertalized thats all keep it watered and give it a bit of time and it will come back up green it burned the lawn. The thing is those spots that turned brown didn't need fertilizer they were good.