I would say the cable is messed up.
Hi! I have the broken Asus HD2 and a USB/Serial Cable connected. I know my connector (rx,tx,gnd) but tried to find the right pins at the box. I used your introduction ... could find the GNX from the box, because I recieved many spaces within seconds. then I tried combinations from my TX+RX with box PINS until I could recieve letters I sent via my TX (trough the box..) .. so I think that 3 PINS must be correct. After reboot I got a correct boot-display with Realtek-prompt... But after every letter I press/send I get of course this letter displayed in hyperterminal, but two new line feeds as well. So I cann't complete any command!
(I just pressed "ZRD"!)
What's wrong there? I didn't used the 4th PIN from the box.