If you boot it up with the power supply connected and disconnect it when windows is running does it go off aswell?
If yes then I would guess that something like the battery charging circuit on the mainboard is defective, so your best chance is the support from the place you bought it from.
If they don’t offer you warranty repair/replacement you could open up the tablet and measure the voltages of the lithium packs with a multimeter, (which would void your warranty, but I guess if they don’t want to repair the tablet, it does not matter).
Greeting
Benjamin