Try tu use AltBoot method to upgrade your machine. For this:
-Create a folder on a USB thumb drive named AltBoot
-Copy the unzipped firmware file sw#072.xxx.xxx.xxxxx#.DLM into the AltBoot folder
-Power off and insert the USB drive into one USB port of the machine
-Power on the machine and wait for the Software Upgrade screen to appear
The software upgrade may take up to 60 minutes to complete. Folllow the screen instruction to remove the USB drive and to press 0 (zero) button. The system will reboot several times before returning into a Ready state. It is possible a seccond upgrade screen to appear.