phone wont turn. when inserting new battery camera LED flash once

hi,

a frind of mine gifted me a "faulty" lumia 550. he said one day it would turn on anymore. i thought it was the battery and ordered a new one. now when i insert the new battery the camera led flashes once and nothing else happens. the phone wont turn on als it does not vibrate or show something on the display.

pressed volume down and power for 15 sec and volume down and up plus power buton for 15 sec. no reveal.

would could it be?

thx