I also have a similar problem with my Teclast Tbook 16 Pro…
I lost the startup boot selector since some Windows 10 mandatory update, so I no longer can choose between Windows 10 or Android at power on.
And recently I lost Android over an OTA update… when it boots it just stays on teclast logo forever…
I’ve tried to do a factory reset on android with no luck… I can acess menu by pressing power button + volume down, but the factory reset does nothing.
I’ve contacted Teclast support today via facebook page and twitter but still no answer 🙁
Also tried to download the firmware for this tablet on http://www.teclast.com/en/firmware/ inserted my product ID number but the I got error 429 from dropbox 🙁
https://www.dropbox.com/sh/obgcuiiybavspfk/AAD8nF_n43JYaRO2-kM0fpRVa?dl=0
Apparently their dropbox quota has been exceeded and it’s been like this for 3 straight days now.
So if I were you, I would try to do a factory reset until at least we can get hands on the firmware file because without it I think you risk loosing everything if anything goes wrong (so far I lost Android).
If I have any development on my side I’ll post it