Hi,
the same thing was happen to me yesterday.
I used my tablet with bios v.1.62 (from 4pda.ru) for several months with no problems.
Yesterday I switched off the tablet and after recharging it starts to bios only.
Try to reflash your bios like described here http://techtablets.com/2015/10/teclast-x98-pro-boot-to-bios-missing-emmc-fix-bios-update/ and in doc-file in the archive.
It works for me 🙂