Alright, did not see your grub.cfg and fstab earlier. (if you just edit- we won't know you had a new post)
And its' confusing because I thought you messed up and cannot boot windows. And in trying to fix it you messed up manjaro.
Never mind, we start again....
To recap, there is no longer any windows (and don't mind).
Objective - You are trying to boot to sdb6 (uuid 2a77xxxxxx)
Your sda drive - ? what do you want? what linux and you want to boot this also?
But let's start with just booting sdb6 as our final objective.
You have an sdc (super grub - you say). Remove that and just make sure its just sda and sdb only.
sdb is external usb or internal hard drive?
Start here
Make sure sda and sdb is always connected. remove other drives like sdc.
Boot up a livecd dvd. (can be any linux with grub2) and in boot-legacy mode.
When booted, at terminal check where the sdb6 is by "sudo blkid": meaning is it listed as sdb6 with that uuid?
Then if trully is sdb6, then
sudo mount /dev/sdb6 /mnt
sudo grub-install --boot-directory=/mnt/boot /dev/sda
Remove livecd and boot normally (do not need to set boot to any drive- just let boot from computer start - do not adjust bios settings)
If your grub.cfg is okay, you will get to grub menu and bootup.
If not, you will get to grub prompt (grub>) and it's okay. Don't worry.
If grub prompt, type and press enter afeter each line.
grub> insmod part_msdos
grub> insmod ext2
grub> search --fs-uuid --set=root 2a772c73-63db-4668-a69b-af6e295954e2
grub> linux /boot/vmlinuz-3.16-x86_64 root=UUID=2a772c73-63db-4668-a69b-af6e295954e2 rw
grub> initrd /boot/initramfs-3.16-x86_64.img
grub> boot
When booted, open terminal and
sudo grub-install /dev/sda
sudo update-grub
NOTE: if grub menu appears, and pressing enter at entry does not boot,
boot again and this time, press 'c' to go to grub prompt, and type manually as above.
[tip] - use <tab> for auto-completion but make sure initramfs-3.16-x86_64.img end with .img (easy to miss out if using <tab>)
