What baud rate/serial settings are you using?
It should be 9600 baud, 8 data bits, 1 stop bit, no parity.
That description sounds like it could possibly be a baud rate mismatch.
Edit: Never mind, I just saw that you can console in to another one just fine. Sounds like the serial port on that switch may have gone bad. I'd suggest opening up an RMA for that switch.