I fixed mine. Here is my thought process to troubleshoot. Battery charges to 100% but no buttons work, holding them for ten minutes does nothing. So we know the battery is good and the screen is fine. So whats left? Either the mobo is fried or it's mechanical. I opened it up using the directions from the iFixit website. I found the ribbon connector to the power button, popped it loose and re-seated it. Voila! Phone works! It's a 3 year old Droid Moto Z Force XT650-2. All those guys that have the same problem, try this. It's a tiny matchhead size connector and they get loose or corroded over time. It's been a month, still working. By the way, this is my second screen and second battery. The quality control for this phone is horrible. Or deliberate. Mine, like so many others, lasted a year and a day. Coincidence? I dont think so!!!