Unexplainable behaviour, Constant Crash

Hello,

This is my last shot before buying a nokia lumia 930...
I bought a HTC one (m7) 2.6 years ago.
I was happy about it but the camera didnt work, had to send it in 4 times and atlast i received a replacement HTC one ( other color but hey it worked right).
the replacement phone is now 6 months old.
One week ago i had the constant boot loop problem ( Phone powers off, boot, htc logo, power off , boot , .... )
I already fixed this problem once 3 months ago and worked back fine for 3 more months until now.

All the backstory behind here comes the deal:
*Can only turn on phone while it is plugged into a pc
*when booted: crashes on setup, changing volume, refreshing blinkfeed
*if not plugged in => cant boot
*does crash at same time on boot ( if not plugged in) => looping
*tried 3 different roms, all the same problem

personally i think this is a hardware problem but i have no idea where to start ...
You guys have any tips, suggestions, experience with this abomination phone ?

ps. waranty expired cause its only the waranty of the phone when bought that counts

Sincere greetings,
Brock