Hi @nesredin ,
Try removing the battery from the phone and then holding the power button for 15 seconds and then let it go. Replace the battery (look for the connectors at one end so that you re-insert it the correct way), replace the back cover and then try turning it on.
Here's a [https://www.youtube.com/watch?v=6jCvGFTBF4E|video] that may help. The battery is seen removed in the first 24 seconds