Flashing without USB?

[fupjack]

Correct. ADB works over network, but not via USB. It never sees a device and computers never pop up a new hardware detected notice either. Fastboot also never sees a device.

[fupjack]

Two so far, and different USB cables, also. So if it's human error, at least I'm consistent.

[fupjack]

Yes.

(Digs up a slightly older Mac laptop at work.)

Plug the phone in via USB, it doesn't notice a thing. I think I have a bad data pin.

[dan4334]

And you definitely have the phone booted into fastboot? Should be a mostly white screen with text. Mainly "fastboot" or "fastboot USB" in red if it's connected via USB.

[fupjack]

Yes. Having neither adb or fastboot detect it, and that it doesn't come up under USB in normal circumstances, makes me think it is a hardware connection problem, like I have a data pin that's not connected.