Boots always into fastboot after very long boot-time

He guys,

I can't start my T-Mobil branded Htc one sv (unmodified, everything stock and locked)

Every time I power on the phone there is a very very long boot time (up to 3min) and after this I'm in the bootloader.
Also fastboot commands with direct reboot into bootloader or fastboot leads to the full boot-time like I would do a normal boot.

HTC-Screen -> HTC-Screen with Beats by Dr.Dre -> T-Mobile-Screen -> bootloader

All resets are pointless.
If I enter recovery I can see the blackscreen with the icon in the middle, but there is no menu with options.

I can't unlock the bootloader. If I use the official unlock file I can enter the unlock-menu but if I select "yes" it starts the long boot-phase which ends in a still locked bootloader.

So I'm unable to install anything.

In recovery is also no adb available.

I tried to install a RUU but this always fails because the reboot directly into fastboot doesn't work (So this is my explanation)

So I have no idea what I can do. I think it's a hardware damage but I'm not sure how to check this.


Any ideas if I can do anything or should I just say goodbye ;)

Thanks for your help
Julian