One M7 cannot pass bootloader with replacement display

Hi everyone,

I habe a weird problem with my M7.

It has broken frontglas, but the lcd an touch are working well. Now I wanted to give it to my father as present, but with a fixed glas.

I ordered a replacement part (fronthousing + display + touch).

When I connect the display (just the flexcable next to the battery flex) the device turn on, but after displaying the bootloader image the screen turns black, but the backlight keeps shining.

When I try to enter the bootloader menu it works without any problem. I can navigate there and fastboot works fine.

When I try to boot into recovery mode the screen stops changeing displaying the "entering recovery" screen.

I also waited for some minutes... nothing happened.

When I reconnect the original display, everything works fine again.

First I thought that the replacement part was broken so I sent it back and bought a new one from another seller, but the same thing is happening again.

I already tried flashing different roms and recoverys ( newst HTC Stock and newest CM 11; CWM and TWRP), but that made no difference.

Does somebody have any idea?

You think it would be worth investing in sunshine s-off and trying different hboot versions or turning it into the google play version?

Thank you :)