Your grass all died because you attempted to over-seeding in the middle of summer. Over-seeding is best done in late September and October for my area in the mid-Atlantic. I don't know what zone your in, but I can't think of any area, except maybe Alaska
where you would try to establish new grass in July.
Most new grasses germinate best with a soil temperature around 65-75f and plenty of water. Both of those conditions were practically non-existent in the lower 48 for the past 3-4 months.
Get ready to hit the weeds with Round-Up and try again next month. I think you'll see some better results. Where are you located?