Flashing vu zero 4k problem

Hi guys. I've a problem to flash my vu zero 4k. I do everything as it is in instruction and all process going as it is described. After all is done and I restart my box it's only show new softwares bord on the screen for couple seconds and then reboot to original soft. No matter what soft, I try a number of them, the symptoms are the same. Any clue what am I doing wrong? TIA

Thanks a lot. Different pendrive did the job