I think I messed up big time with my BIOS (I changed the UEFI setting to legacy) and now I can't access my BIOS. After changing it I lost the access to my Ubuntu and was forced to install a new OS, which is Lubuntu 18.10 which seems very buggy and I can't repair, it is starting to look easier to install another distro like Ubuntu 18.04 again than having it.

I managed to be able to open the GRUB but I still can't access the BIOS (I tried every key possible and previous to this F2 was my access key to the BIOS).

As of right now I have tried to fix the BIOS by doing this, but it did not work. Also I have tried to use rEFInd but it returns EFI variables are not supported on this system. when I try to install it. I have saw multiple posts saying I could try to boot an USB using the GRUB but I am scared to fully following them because of the difference between what they ask to look into the grub files and what I have in my file.

EDIT: This is what doing a sudo parted -l returns

Partition Table: unknown

Disk Flags: 



Model: SAMSUNG MZVLB256HAHQ-00000 (nvme)

Disk /dev/nvme0n1: 256GB

Sector size (logical/physical): 512B/512B

Partition Table: msdos

Disk Flags: 



Number  Start   End    Size   Type     File system  Flags

 1      1049kB  256GB  256GB  primary  ext4

Big EDIT:

My PC's model - Motherboard model: xmakb3m0p100b

I've also executed tree /boot/ to see what I have in my boot and here is the result and also tried to run the Boot-Repair tool, which did literally nothing.

I've also tried UNetBootin with both Fedora 29 and Ubuntu 18.04 and I get this when trying to load any of the new tabs available in the grub:

error: hd15 cannot get C/H/S values.



error: you need to load the kernel first.

Tried also to do the grml but whenever I try to enter the distro I have downloaded (Fedora) it go to a black screen and then back to the grub, maybe because I am in legacy mode?

I tried once more the rfEFInd doing this:

sudo refind-install

ShimSource is none

Installing rEFInd on Linux....

The ESP doesn't seem to be mounted! Trying to find it....

// doesn't seem to be on a VFAT filesystem. The ESP must be

mounted at //boot or //boot/efi and it must be VFAT! Aborting!

The computer appears to be running in BIOS mode and has no ESP. You should

create an ESP, and ideally boot in EFI mode, before installing rEFInd.

I don't know how to create an ESP nor boot in EFI after changing the BIOS to legacy. I have tried to boot my USB stick by following this but when I tried to chainloader /efi/boot/bootx64.efi it returned error:invalid signature - which seems correct since I am in legacy mode and not in UEFI mode. I've read that I could remove my CMOS battery to reset to defaults but I wanted to try everything I could before doing it.