Boot partition not detected in Bios

Solution 1:

1. Download the Boot Repair iso file.

2. Make a bootable Boot Repair live USB flash drive with Rufus or UNetbootin. If you have a Debian-based distribution handy you can also use Startup Disk Creator to make a bootable Boot Repair live USB flash drive.

3. Boot from the Ubuntu USB flash drive and install the OS until you get to this error message.

   The 'grub-efi-amd-64-signed' package failed to install into /target/.   
   Without the GRUB boot loader, the installed system will not boot  
   

   Continue the installation anyway until it finishes.

4. Reboot the computer with the bootable Boot Repair live USB flash drive selected as the first entry in the boot priority menu of the UEFI/BIOS.

5. Click the Recommended repair button in the Boot Repair menu and run it. You don't need to click any of the Advanced options.

6. Reboot to the Ubuntu installer from the Ubuntu USB installation media.

7. At the Installation type screen select the Replace ... with Ubuntu option where ... is whatever Linux you installed the last time. The Ubuntu installer may identify this Linux as "generic Linux" instead of Ubuntu because it has a different bootloader which was installed there by Boot Repair. This time the installer will run all the way through until the end and replace the grub that Boot Repair installed with the appropriate grub for Ubuntu.

Converting Ubuntu into UEFI mode

1. Start Boot-Repair, and select Advanced options -> GRUB location tab.
2. If you do not see a Separate /boot/efi partition option, this means that your PC does not have any UEFI partition.

3. If you see a Separate /boot/efi partition option, put a checkmark in the checkbox to the left of it, then click the Apply button in the lower right corner.

   

4. Set up your BIOS so that it boots the hard drive in UEFI mode. The way to adjust this setting depends on the specific model of the computer, but generally this setting is located in the boot priority settings under the Boot tab of the BIOS/UEFI setup utility.

For more information about converting Ubuntu into UEFI mode review https://help.ubuntu.com/community/UEFI in the section about Converting Ubuntu into UEFI mode.