Okay... some more info.
I've tried shorting pins 3 and 8 on the com port on the back of this thing to reset it, but it doesn't seem to be working. The M1 light should flash several times quickly and then return to the steady once-per-second blinking. Instead, after I start it up with M1 shorted, it flashes quickly a few times, then starts flashing really, really quickly and doesn't stop. I've also tried shorting pins 4 and 8 and it didn't help.
If I turn it off and then turn it on again, and then plug it into my laptop... the laptop detects a 100MB/s LAN connection, but I can't access the router at the default address via either ping, http, or ftp. Running the firmware upgrade again doesn't detect any router attached to the laptop.
Is there any way to figure out what address the device is currently set to? Or do I just need to send this thing back?