Any chance you could locate an old/free ATX PSU to try out? That would allow you to eliminate the motherboard/software as being the cause.
I'm actually running on a SFX 450 PSU, on that it boots and everything including usb ports work. But when I plug my HD plex 250W or HD plex 160W into the motherboard running off the Dell 240W brick it boots up everything runs fine i can get into windows...but none of the USB ports on the motherboard works....been scratching my head on this for a while now.