iPad won't start - need help

Hi,

two weeks ago my iPad 4 shutdown automatically (battery status ~60%) and now it won't start anymore - the screens remains black.

What I already try:

- Home + Powerbutton at the same time (various methods tested)

- new wall charger (Original Apple 12W)

- new lightning cable

- new battery installed

It would be very nice if anybody has another idea which could bring my iPad back to life :)

Thanks in advance!

P.s. Sorry for my bad english ;)