I think that the cause of the defect may be a hardware failure. You should check useability of your eMMC disk first of all. To do this, you must use any of the available WinPE USB drives with utilities to check your device.
Instead of this, you can go on an even easier way. You can flash both systems by clean install. First you need to flash the Android with a full cleaning (flash.json), then do Windows. Keep in mind that using this method you will lose all your files in the tablet irrevocably.
If at least one of the systems works propelly after a successful flashing, you can consider yourself a lucky one.