Hp Elitebook 850 G3 Not turning on

[Nickuy]

Hello,

My elitebook 850 g3 won't start. I spend days searching on forums, google, youtube, hp but can't find any working solution yet. I tried the hard reset and many other button combinations. Only thing i didn't try is removing the sealed off battery yet because i get a led blinking code where i cant find the meaning for. Thanks in advance for those wanting to help me, for your time and help. I'll describe the problem as good as possible:

So here's the problem:
1. I press the power on button and it flashes white every 7 seconds. At the same time at the top right the wifi led blinks orange and the mute led blinks white. I cant hear any sounds of the laptop starting and it keeps blinking every 7 seconds for hours untill i think the laptop battery charge is empty.

2. I also got 4 leds at the bottom left of the elitebook that flashes together with number 1 within the same 7 seconds time, from left to right its a wifi led, power led, charge led and a disk led. Firstly the charge led blinks very fast from white to orange to white to orange ( 2 seconds) and after that very fast the wifi led blinks orange together with a white power led and a orange disk led (1 second). This keeps repeating together with the leds at number 1 so for 4 seconds theres no led down left blinking until the power led at the top left blinks again from the 7 seconds interval.

3. While charging with the AC plugged in it seems that the charge led at the bottom left sometimes stays orange for around 20 minutes and then it falls out and sometimes there's no led at all. After a hard reset the same led stays white for 10 seconds with the AC plugged in and falls out after that.

I also noticed that when i try to power the laptop on by holding the power button for 10 seconds that the top left power led together with the shift lock led turn on for 2 seconds and then fall out no leds blinking anymore.

Anyone knows what all this means? I'm so grateful for any help around this case since i'm a remote digital traveler and i really can use my laptop. feel free to ask any more information if something in my description is not clear enough or missing.

Kind regards and many thanks!