Sooooo… i have 2 drives, and one and half 
I was using for Windows 10 and today i decided to finally separate the 2 of them so now i got one drive with windows and one with Linux and well, after that grub wasn’t working anymore no screen to select Manjaro or Windows etc. Got in the recovery mode then needed to set the root and the prefix , grub sets root to (hd0,gp3) and not (hd0,gpt2) 
soooo i need some ideas please
well maybe using the installation usb again and reinstating grub can work?