Cannot find bootable device - can't boot from USB - can't update BIOS

Hi guys,
I was wondering if anyone could give me some advice on how to proceed with this faulty installation.
I have Dell Inspiron 15 5570 that had a while ago Linux Mint installation on it. The installation wasn’t good, I didn’t use the laptop for a while and when I got back to it and wanted to set it up properly, I couldn’t do anything that I wanted.

The problem is that the Bios won’t accept usb devices plugged in. In boot options it only shows “ubuntu” and “ MocksbSet”. Adding a boot option doesn’t change a thing.

Ubuntu option is set to look for boot in /EFI/ubuntu/ and I can't change that either.

Disabling the Secure Boot and enabling Legacy Boot options doesn’t do anything. Basically, any changes I make to BIOS are not persisted. I tried flashing the BIOS but that didn’t work either. BIOS  remains on same version .
I tried clearing CMOS but it didn’t help whatsoever.

When I boot my laptop I manage to get to the Grub Rescue prompt. I tried listing my drives(including usb live installation which is visible from there) and setting up the proper one in prefix and root, but running

insmod normal

Or

insmod linux

Doesn’t do anything. Calling normal or linux commands afterward just returns:

normal command not found.

All the diagnostic tests on the laptop pass without any problems.
What I tried doing after that is to take the ssd and hook it up externally to a computer and install Linux there. I installed ubuntu twice, with different partitioning and boot locations but when I put the hard drive back in the laptop and start the system, I can’t even get it to recognise hard drive as a bootable option. The only things I can do is to test the hardware, see boot options and that’s it.

Is there any way I can get grub at least
Has anyone come along a problem like this or if anyone has an idea what I could try next, it would be really appreciated!
Thanks!