Sounds unrelated to the BIOS update. When you push the power button, does the light come on, or does it act like it wasn't even pushed? Try removing any unnecessary devices - any external devices, expansion cards, drives, all but one memory stick in the first slot, etc.  Try clearing the NVRAM using the jumpers on the motherboard.  If still nothing, try reseating the processors, and/or trying them one at a time in the first slot.
Heres exactly what I did. I updated the BIOS using an executable file provided by Dell.  After booting from bootable USB, it restarted and confirmed that the BIOS has been revised. I disconnected the server and moved it to another room.  I plugged it in, hooked it to the monitor, and now when I press the power button....nothing happens.  It doesn't even try to power on.  Just silence.  Please advise!!!!!!!!!!!!!!!!!!!
R410 won't power on after I updated the BIOS.