The definitive guide on how to upgrade your Dell Precision 5820 to v2.4 BIOS

Unplug your 4k monitors

Plug-in a “low-res” FullHD Monitor (1080p)

Run the update — it will work, and will no longer be stuck at 0% or 100%

Finish the BIOS update (it takes a few minutes)

Wait for it to completely finish

You are done!

PS: If this does not work, unplug your USB devices during the update (just after you press the OK button to update the BIOS).