I have a Pi-Top I just assembled, with a Pi 3. When powered on it looks like a normal Linux boot sequence. A bunch of [ OK ] messages go scrolling by and there is a little green light on the raspberry pi. There is a faint green circle around the power button on the Pi-Top.
After a few seconds it just turns off, I think. The screen goes blank and the light on the Pi goes out, but the green circle around the power button stays on.
I tried swapping out the USB cable between the hub and power the Pi and upgrading the software on the sd card to 2017-02-23-pi-topOS.img.
I don't see any faint green circle - my power button shows as an upper semi-circle illuminated plus some stray illumination above it.
It sounds, to me, like a power problem.
I have also run run my Pi together with the SDcard away from the pi-top enclosure. Given a power feed, screen and mouse/keyboard it can boot up and run successfully on a 'normal' display.
I tried with and without the external power adapter it came with, then I tried using a phone USB charger for an external power source, but I couldn't figure out if it was booting and I had no video, or if it simply wasn't booting and I didn't know how to power it on.
I tried disconnecting the GPIO cable and it worked booting to a new a desktop. If it is optional, what does it do?
Should I just buy a new cable, or should I be worried about a damaged Pi or Pi-Top Hub? If so how do I test?
FYI - the faint green circle is just a green light behind the power button shining through the gap between the power button and the chassis.
The GPIO connection gives access to the I2C bus, and can thereby get the battery status. It also, from what I have read, allows certain special key functions (see getting it to act like a Pi).
If your disconnection exercise allowed booting to a visible display, then the GPIO connection must be either wrong or the cable. I don't know how you could decide, but remember worrying about some of the cable connections being able to be made wrongly.
I suggest you ask for support by entering a ticket.