can you catch the computer during boot up when the dell logo appears, and press F12 and get the computer to boot from the NIC card? if you don’t get the option to boot from the NIC card it isn’t enabled in the BIOS settings.
I just had this same problem with some brand new Dells. There is also a deep sleep mode in some Dell BIOS that needs to be turned off. Without this disabled, the NIC card isn’t even powered on to look for WOL packets.