I just had an issue where windows boot manager was just not playing nice. If you can load into your bios and look for a boot override to boot into manjaro you may be able to access a terminal to fix your issue. Just be careful in the bios.
For my issue I had to turn off fastboot, then turn on eufi (secure boot) so I could access the majaro boot screen where I could choose to boot from windows or manjaro. The easiest way to do it was from a boot override located on my exit screen in the bios. Boot override means it ignores the boot priority (probably set by windows boot manager on the last update), and boots directly from the chosen partition (the one with manjaro).
I hope this is helpful.