hmmmm… the only times this has happened to me were (A) when the firmware had the SD driver crash bug, which meant the unit often started up just fine and (B) when the firmware installation didn’t actually work.
To check the firmware install I usually try to be monitoring the output of W/ as I install the firmware, so I listen for the pretty tune and once the firmware completes there’s a short, high-pitched beep.
Aside from that I’d say you should contact Mannequins in case it’s a problem with your unit?