Onyx Boox M96 Died

2 years and a few months after purchase, my Onyx Boox M96 died for an unknown reason. There was no crashing or smashing, only gentle touches.

When I press the ON button, the light briefly flashes (orange, violet), and turns off. It seems the battery is depleted. But: When I connect it to the computer via USB cable, there is no reaction what so ever. I have tried different USB cables, and different chargers and PC USB. But no reaction. Nothing.

Any advice, please?