Hi, i replied to this discussion: http://midibox.org/forums/topic/19987-goom-stm32f4-usb-problems/ but i guess the board is a better place for it? Maybe someone could move it here. In short, the original poster and me both have similar problems with the new stm32f4 discovery pcb (STM32F407G-DISC1). The app will not run if only powered from micro usb; i think it has to do with a new ST-Link (ST-LINK V2A compared to the old ST-LINKV2)  that is on the newer boards. According to