Welcome to the forum! 
Since you’re a new user on this forum, I’d recommend you check this out:
Please boot from a Manjaro live environment and provide further information as per above.
From what you described in your OP, it sounds like your BIOS/UEFI is corrupted. There is a chance that you installed Manjaro over the BIOS already corrupted and then the issue became evident after installing Manjaro. This might be the result of abrupt power-offs, among other hardware misuse. In that case, best course of action is to follow the BIOS recovery procedures from your hardware manufacturer.
Also, I would like to give you an introduction to the forum rules. Please note that this thread may be closed if deemed off-topic as per rules.