Wow, I'm at a loss of ideas, especially after someone else had success this morning.
Are you sure that you've connected:
- TX <-> RX
- RX <-> TX
- GND <-> GND
If you have to power your USB-to-Serial converter, be sure to apply power to the converter.
No other cables should be connected.
- To reiterate, do not apply any TTL/Serial power to the router. Only connect TX, RX and GND!
- Be sure that the USB port used has enough power to run the adapter!