I've got a Chinese tablet that boots properly up to the unlock screen, where if I'm quick I can unlock, I can see wifi is connected, etc. but around that point it completely freeze, even the power button doesn't turn off the creen and I have to reset it by long pressing the power button.
I tried all combinations of keys to bring up a recovery (power + volumes) without luck so far. If I press any volume or back key while powering up, the tablet doesn't power up and stays black. adb isn't finding the tablet. I opened the tablet, there are pins to connect a rx/tx serial. I could do connect a serial adapter to it if that could be of any help.
Actually, at this point I don't care much about the tablet but that could be a good opportunity to start learning a bit more about Android hardware development, just don't know exactly where to start.