Sanguino Motherboard not powered via USB?

I had my Sanguino mobo with extruder controller working two days ago when I started having connectivity issues with the motherboard.

When I have the motherboard only plugged into the USB -> serial, the mobo does not power. When I plug my USB -> serial into my extruder controller, the extruder controller does power.

Finally, when I power my motherboard via the ATX connection, both the motherboard and the extruder controller power on but I cannot connect to the mobo.

I'm pretty sure that I should be able to connect without the power supply attached. Does anyone have any ideas?

Thanks,
Adam

I just tested my Makerbot Motherboard 1.2, and it doesn't power when I plug in the USB cable only. I think there's a jumper you can populate if you want it to do that, but in the default configuration you need to supply power via the ATX connector before you can talk to it.

The extruder controller is different - it gets power from the USB cable. Watch out - I've had my computer spontaneously shutdown when I had the extruder controller connected to both a powered up motherboard, and my my computer via the FTDI USB cable. Noise on the 5V line seems to be the culprit, which is probably why the motherboard doesn't share the 5V line.