dethatching help

I have bought power rack de-thatching for the mower. I used it on the lawn and it seems to cut the lawn down to nothing? What did I do wrong? I am not good at this lawn stuff.

 

i bought a pull-behind dethatcher rake this spring. i ran it back-and-forth and back-and-forth until my yard looked like a tornado had gone through it. tehn i fertilized. i had lots of areas that were almost bare. now, six months later i have a lush, full carpet of grass. in previous years i had fertilized without the dethatching and i did not get nearly the same results. my only concern is that you may be a little late in the season. i will defer to those that do this for a living in your area to give you the go-ahead.
good luck!