What's installed on your eMMC? If this occurred after installing Manjaro to the eMMC, then you probably need to wipe it and reinstall. Easiest way to make that possible without the adapter or UART cable (at least in my opinion) would be to:
-Determine a working surface where you can take the bottom casing of PBP off.
-Place a soft material down by the edge of your surface, and lay the PBP keyboard tray onto it. The screen should be hanging off the edge, upside down. (I suggest doing this so that you don't have to worry about damaging the case by opening the lid w/o the bottom casing.)
-Remove the bottom casing (be sure to read the wiki for various precautions beforehand.)
-Flip the eMMC switch to OFF.
-Put the PBP on its side, so you can access the Power key.
-Insert your Manjaro installer SD card.
-Turn on the PBP.
-Once you see the PBP booting off of the SD, flip the eMMC switch back on.
-Use your Manjaro SD to either wipe the eMMC and shutdown (so you can put the PBP back together, boot back into the SD and try installing again.)
-Determine a working surface where you can take the bottom casing of PBP off.
-Place a soft material down by the edge of your surface, and lay the PBP keyboard tray onto it. The screen should be hanging off the edge, upside down. (I suggest doing this so that you don't have to worry about damaging the case by opening the lid w/o the bottom casing.)
-Remove the bottom casing (be sure to read the wiki for various precautions beforehand.)
-Flip the eMMC switch to OFF.
-Put the PBP on its side, so you can access the Power key.
-Insert your Manjaro installer SD card.
-Turn on the PBP.
-Once you see the PBP booting off of the SD, flip the eMMC switch back on.
-Use your Manjaro SD to either wipe the eMMC and shutdown (so you can put the PBP back together, boot back into the SD and try installing again.)