I seem to have a similar issue to someone else, but I could not post on that thread, where the Pi Top does not make it to the standard Linux boot up screen (drivers etc). I get a blank screen.
I have included a picture of my Pi Top, just in case one of my connectors don't look right to an expert.
40 pin unplugged from the RasPi end. check
HDMI cables, I redid them a couple of times. Pushing them in as much as I could.
1. red and green both on for a few seconds
2. red stays solid on. green blinks a few times then goes off.
3. red stays solid on. after a few more seconds the green blinks a few times then goes off.
Make sure the hub is seated good into the socket. Seams like you did everything else except create a ticket on it. Perhaps try a fresh install of Raspian on a different card?
I have tried to get my display on my newly created Pi-Top to display something and have run out of ideas. I know the keyboard unit is working, the pi boots correctly (when I connect my HDMI monitor to it is works fine). The bright-dark button on the keyboard does brighten/darken the display but no display (apart from the powered-up glow) results.
My school bought two (a green one and a grey one, with the possible view of buying class sets of these machines) and the first PiTop (green) assembled fine, but was missing the RasberryPi, SD card and power flex in it's packaging. We used one of our other R-Pis and it works fully.
The grey one arrived complete, we used the same construction method but the screen is devoid of words.
I am concerned about build quality, dispatch checking and level of support so far - hopefully we will get at least a response about the missing items - not sure how to move forward on display issue however - created a ticket, fingers crossed
I have contacted Piu-Top support and have begun a process of remediation - all very promising
Same issue with at least 2 out of 8 purchased pi-Tops. 2 worked fine, next 2 blnk screens. I have done all suggested checks above without success.
I have something similar - I downloaded to a regular SD card and put into my regular pi hooked up to my home monitor. First few times I booted and though the screen initially picked up something I never got to the pi boot sequence.
Then I went into the config settings and commented out the force HDMI over DVI and viola, the boot sequence came on. However, I'm now not able to get past the pi-top branding screen which appears directly after boot.