How to diagnose a frozen screen

I recently got a Kindle with the screen stuck in the loading screen (not reading a book under a tree with a loading bar) no matter what I do.

I tried using the Kubrick tool found here, which went through successfully.

So now I have a Kindle with a fresh firmware 3.4 but the screen is still unresponsive.

Considering I was able to put the Kindle in download mode and flash something, I don’t think it’s a motherboard fault like in this thread.

I suspect it may be the e-ink display but I don’t want to order it online just yet if I’m not sure, partly because I don’t trust the build quality of random Chinese sellers on the internet - I’m assuming the OEM part is of a better quality, so if there’s nothing wrong with it, I hope to keep using it.

Other clues I’ve gathered are that despite charging for really quite long, I don’t get a green LED (in the above iFixit thread, the user mentions getting a green LED after fully charged)

I read somewhere that you can control the screen using the UART. I don’t mind trying that if I knew how haha

If anyone has any suggestions for me to fix this I’d greatly appreciate it.