iPhone 6 dead after display replacement

I replaced the display of my iPhone 6. Once I was finished I turned it on. The phone worked fine but the Home Button mechanism didn't make the "klick"-Sound. So I unplugged the display again to fix the problem.

The problem solved I plugged everything back on and nothing happened. The display remained black and the logic board was getting hot.

I checked the plugs and it looked fine.

Even the broken display remained black after putting it back on and the Phone seemed to be dead.

There also is no vibration when neither turning it on, pushing the home and power button 10 seconds nor connecting it to the PC.

iTunes does not recognize my phone either.

Furthermore I can tell it is not a case of the "the long screw problem"!

I hope I could give you an insight into my problem.

What are your solutions or recommendations?

Is the phone hopelessly lost?

Thanks for your help