I'm leaving this here for now just for reference.
Forget installing Mint on old hardware.
Installing Linux On Old PC - Avoiding UEFI
Why? Because your BIOS doesn't handle UEFI but current installs default to it.
In the Linux live system open Gparted and partition the destination to msdos and fomat ext4
On install:
Select "Something Else": In the installer type selection, DO NOT choose "Erase disk". Choose "Something Else" (Manual Partitioning).
Assign the Partition:
Click on your existing ext4 partition.
Click Change.
Set Use as: Ext4 journaling file system.
Set Mount point: /.
Ensure the Format box is checked
Bootloader Location:
At the bottom, ensure "Device for boot loader installation" is set to /dev/sda (the drive itself), NOT /dev/sda1.
Ignore the Warning:
When you click "Install Now", it will warn: "No EFI system partition was found."
This is expected. Click Continue.
Sadly it probably will not boot but at least it is installed correctly.
Fix Grub
sudo mount /dev/sda1 /mnt
(Note: Since you have only one partition, your root is /dev/sda1. If you have a separate /boot, mount that too, but usually not needed for single partition setups).
Reinstall GRUB to the MBR:
sudo grub-install --boot-directory=/mnt/boot /dev/sda
Crucial: Notice the command ends with /dev/sda (the drive), NOT /dev/sda1 (the partition).
If successful, it will say Installation finished. No error reported.
Generate the Config:
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
update-grub
exit
Reboot: Remove the USB and restart.
Oh No! I don't have an account.
Restart and hold Shift (or press Esc) to see the GRUB menu.
Select Advanced options for Linux Mint.
Choose the line ending with (recovery mode).
In the menu that appears, select root (Drop to root shell prompt).
You will be at a command prompt like root@mint:~#.
2. Create Your User Account
Once you have the root prompt (#), run these commands (replace yourname with your desired username):
Create the user and home directory:
adduser -m yourname
(Follow the prompts to set a password and fill in details. You can press Enter to skip details).
Give yourself admin (sudo) privileges:
usermod -aG sudo yourname
(Note: On some older Mint versions, the group might be admin instead of sudo. If sudo fails, try usermod -aG admin yourname).
Fix Ownership (Critical): Since you installed as root, your home folder might be owned by root. Fix this:
chown -R yourname:yourname /home/yourname
Reboot:
reboot
You should now be able to log in as yourname with full admin rights.