Struggling to boot up

[Depau]

Hi, I found a solution for my issue, so I guess you could try that as well.

mrfixit suggested on IRC to see if it boots with the ribbon cable going to the SD card daughterboard disconnected. If it does, try reconnecting it. It might have come loose during shipping.

Thanks to mrfixit2001, anarsoul and Xalius for helping me pinpoint the issue

[tsago]

Alright, I became too restless waiting for the pineshop-sold usb-emmc adapter, bit the bullet and bought one locally (why didn't I think of that before? Please don't ask me ).
Now that I was able to finally re-flash an image onto the eMMC, both booting off the eMMC and booting off SD card (with eMMC in) work.

I'll mark the thread as resolved now.
Root cause: Unknown human error while messing with data eMMC.