Try to go into the Console screen and enter CTRL ALT T then select Boot options then select System parameters and disable all except for the SMP then save and reboot and see if this works.
Suggested reboot done after disabling ACPI, APM and IO-APIC boot options but still no drivers are loading for the Intel Gigabit ET2 Quad Port Adapter (E1G44ET2). As noted yesterday and since confirmed by your review of my startup logs; DSS V6 sees the ET2 adapter and actually reports it 4 times in C-A-T/Hardware Info/Network Controller as: Intel Corporation Gigabit ET2 Quad Port Server Adapter.
I also tried the additional test scenarios without success, each with the three boot options still disabled:
Scenario #1:
With working Broadcom motherboard port disabled in BIOS.
Scenario #2:
With working Broadcom NIC motherboard port disabled in BIOS.
With working Intel RS2BL080 SAS-600 Raid removed.
Scenario #3:
With working Broadcom NIC motherboard port disabled in BIOS.
With working Intel RS2BL080 SAS-600 Raid removed.
With Intel Gigabit ET2 adapter relocated from a PCI Exp 2.0 x8 slot to a x16 slot.
The scenario #4 test results are the same as with the Dell T5400:
1) the Intel Gigabit ET2 in listed in the GUI's hardware section
2) no drivers are listed for the Gigabit ET2 in the GUI's driver info section