Have you checked out that your Tx is not transmitting or it is transmitting but the Rx is unable to receive it , or Tx is really not transmitting your data ...
For checking the first option use a CRO and place it to the point of pin 2 of your TX 's 9 pin Serial D'sub connector and check there pulses are coming according to your data or not , if yes check 1.continuity of wire , 2. check it is connected to pin 3 of RX Dsub or not , 3. your serial port is open for data receive or not ...
for checking the second option use CRO , make sure that data is not coming to TX port , then check port is open or not , , and atlast do the LOOPBACK concept to check that TX is able to transmit means PIN 2 is ok or not....
OK , BYE and Best of luck to you .....
If you get success then pls let me know.