Unplug the power and let the battery drain to force shutdown - it takes around 2 hours for a fully charged battery to drop below 50% for it to shut down. Once shut down, plug the power back in and let it charge for about 10-20mins for the battery to reach over 50% then boot the machine back up. It will then initiate the BIOS recovery. If you can't wait for 2 hours, you'll have to unscrew the back plate to disconnect the battery.
Hi all needing some help please! I started an update while unplugged with about 25% battery remaining. Before I could plug in the screen went blank - I think the battery died. I connected to power and the power on button is backlit but the screen is still black. There's no charging light present by the charging port. I don't have the ability to remove the battery (if that's what is required).  Are there any solutions people could suggest please?  Thanks.
Lattitude 3520 froze during update.