Recently, the LCD glass screen had shattered on my HTC One, and I had purchased a replacement front and back. Upon transferring the motherboard + the secondary chip to the new housing, I accidentally broke off the flex cable connectors for the LCD screen and SIM card. Upon completion of reassembly, I crossed my fingers as I pressed the power button, only to be met with the initial power-on vibration and no image on the LCD. Unfortunately, I can't verify if the SIM slot is working without the LCD, but I'd assume it isn't.
Anyway, thanks for listening to my story. I've supplemented it with pictures indicating where I messed up. The first picture is the motherboard. Compare the two connectors contained in the red circle. The left one has the white tab, while the right is missing its white tab. The second picture is the SIM connector to the secondary board. As you may notice yet again, the white connector is missing. If anyone has legit/illegit solutions to this problem, I'd love to hear from you.
Thanks in advance!