The seed uses all the stored energy before it can reach the surface and begin producing its own food. Soil dried out or was too wet.
Seed needs moisture to germinate.
Too little and the seed dies. Too much moisture and seeds may get damping-off, a disease problem that causes the seeds to rot and die. Improper soil temperature. Some seeds germinate better when the soil temperature is cool, including spinach, lettuce, and radishes. Other seeds need to have a warm soil to prevent decay, including sweet corn, beans, squash and pumpkins.