try step in this video How to recover from booting issues using the BIOS Recovery Tool | Dell US to see if you have a bios recovery in your 8940.  if still no luck may need to call Dell warranty support. lesson here is if PC is working fine do not heed the call for BIOS update from Dell which has bricked many motherboards.
Hello all, Today I updated my XPS 8940 to the latest BIOS firmware and now my PC will not boot. The install seemed to go fine but now there are issues. It will turn on, my keyboard and mouse will light up my hard drives will turn on, but it will not go past the DELL logo screen. I have tried to access the boot menu (F12) and the bios set up (F2) but these menus will not load either. Everything was working fine until this BIOS update. Has anyone seen this before or have any ideas to fix this?
XPS 8940, will not boot after BIOS update