I already tried lots of things, even took out the internal sdcard and made it empty, restored it from a virtual harddrive and so on. The only thing happening when I press power + volume up is that the screen powers on, goes from white to brighter white, then goes black for a moment and then shows bright white again till eternity. So I guess it is completely dead.
(also tried doing various combinations like power + M button but that didnt help)
I have stock rom from COBY(m801_mtds.img), I can send you a link if you want.