First what you need is a serial console. Get the headphone to USB adaptor, and flip the switch inside the PBP. I forget how it's marked, but it comes from the factory set for audio, and you want to switch it to serial data. You'll need a computer with a terminal emulator that can run at 1,500,000 baud, and work with a USB RS232 device.
Keep the eMMC disabled for now. Try booting any way you can, and see what you get on the terminal.
Someone here reported trouble with the reset button at one point. I wonder if since pressing it, it might have gotten stuck on. But start with the serial console.
Keep the eMMC disabled for now. Try booting any way you can, and see what you get on the terminal.
Someone here reported trouble with the reset button at one point. I wonder if since pressing it, it might have gotten stuck on. But start with the serial console.