Here is a link to the firmware for a vx858 copy player, if may not work but you have nothing to lose if your player is dead.
MP4 Nation Forum :: View topic - DON'T LOAD ONDA FIRMWARE ONTO OEM VER. OEM FIRMWARE HERE
Can you get your player into upgrade mode? if not try this guide:-
MP4 Nation Forum :: View topic - VX858 / VideGo28: Opening & Hard-Recovering 