Intel Boot Agent doesn't allow to enter the BIOS

Try replacing the battery with a new one if it's 5 or more years old.  Be sure to repeatedly press F2 as soon as you power on.  Don't wait for a keyboard light or Dell logo or anything like that.

try reset CMOs jumper which will help you clear cmos settings, then you should be able to press F2 to enter bios and delete NIC boot from boot options.

1. Turn off the computer and disconnect the power cable from the computer.
2. Remove the computer cover.
3. Locate the 2-pin password jumper labeled PSWD on the system board.(blue jumper in lower right corner)
4. Remove the 2-pin jumper plug.
5. Locate the 2-pin CMOS jumper labeled RTCRST on the system board.(right next to blue jumper with RTCRST print on board)
6. Move the 2-pin jumper plug from the password jumper to the pins on the CMOS jumper.
7. Plug the power cable to the computer and wait for 10 seconds for the CMOS to clear.
8. Disconnect the power cable from the computer
9. Move the 2-pin jumper plug back to the password jumper.

The Intel® Boot Agent (IBA) is firmware in the Network Interface Card (NIC). The Intel® Boot Agent (IBA) allows your networked client computer to boot using an image on a remote server.  When the Intel Boot Agent (IBA) is ahead of any other bootable device in the list, it executes and tries to boot the computer over the network.

I followed your step by step instructions but unfortunately it didn't work

Now I'll try to remplace battery for new one...

Shoot.  Does that mean the battery was also replaced?

Now with new battery, the problem persist...

Did you reset CMOs jumper too?  New battery makes sure CMOs settings can be saved but does not by itself correct corrupted setting.  Remove battery for sufficiently long time will theoretically reset CMOs settings too if pc has no power cord connected, but the jumper method is a much faster shortcut.

Do you still have your HDD that did work?  Either way, remove the SSD.  You should be able to access BIOS even with no bootable drive installed.  Can you now get into BIOS?  Load default settings and click apply/save.  Make sure it's also set to AHCI.  If your SSD still doesn't work...

You might have to load a new SSD, or try wiping the one that didn't work using your HDD with Win10 or 7 and disk management in Windows.  Reformatting it wipes it.

If you load SSD or a new one - In BIOS have Secure Boot off and Legacy Option ROMS on.  After it's loaded and working then go back to Legacy Option ROMS off and Secure Boot on.  Be sure SSD is formatted to NTFS.  Win10 will partition for you when loading.  I've only done a couple of Win10 loads and not sure if Win10 already does the NTFS formatting.  I formatted beforehand both times.  Wanted to make sure PC saw drive for loading.

When loading, be sure to have only the drive you want to load installed.

Glad you got it working!!   What a pain that must've been.

In the beginning, you weren't able to boot or get into BIOS.  So how you were you able to update it?  Put the previous bootable drive back in?

cannot access BIOS with drive remove, all says is no bootable device