I had this laptop which came pre-loaded with activated version of Windows 10. It has pretty low specs and so I installed Ubuntu 18 on it (dual boot config). I liked it really as it's pretty smooth and handles my programming loads better than Windows, but since I was skeptical about it during installation, I didn't allocate much space to it. Now, I'm sure I only want Linux on my machine and don't want any Windows. To remove Ubuntu, I did the cmd thing, (list,sel,assign...) in the Windows CMD, not the recovery one since I don't have one. Finally I went to the directory Z:/EFI and there were three folders. Microsoft, Boot and Ubuntu. As the guide stated, I deleted Ubuntu (rm /s Ubuntu). And then I restarted my machine and everything was fine as the GRUB Bootloader menu didn't pop up, it directly booted into Windows.
I then went to Disk Management and deleted the Linux partition and extended my C drive. I had made a bootable USB of Manjaro Cinnamon 18 via Rufus and booted my PC into BIOS and did the required stuff. (Disabled secure boot, changed teh order to boot from USB, USB boot enabled).
But when I try to boot from the USB, I get the error filesystem, GRUB rescue thing. I can boot into Windows fine though, no issues there. Can anyone tell me what I've done wrong? Also, it's be helpful if there was no Windows Recovery Disk involved.