You might need to fix the cables you have to communicate to each other....the pin setting on a DB9 connector is set in such a way that one of the pin (pin2) is set for transmitting signal and one pin (pin3) for receiving signal which goes directly to the other side of the cable.....But you want the receiving end of one of the computers to go to the transmitting pin of the other and vice versa for the sending pin. So you might need to switch the pin setting on the cable if you're using a straight through db9 cable.....I think!!!! At least thats how it works in the ethernet RJ45 cable.