Gino
I'm not sure about our DSL but mine with Road Runner & previosly with the Tel Company uses a Network card and then is connected via a Cat5 cable which looks like a thick telephone wire. I am all most certain this is the type of connector you are using for your DSL modem.
The computer you have sounds perfectly OK for this task and yes It's possible that the comm port may be sharing a IQR. My guess is that that the keyboard may not be set up correctly - so check with some of the Guys here or Email AJ or Dano to make sure you have the Keyboard set up OK.
There are Generally two Comm ports on most modern computers you have to determine which is Comm 1 & Comm 2 which is a trial and error process if they are not labled. Generally it is best to leave the comm port set at 38000 or less unless you hard ware and software telling you other wise.
So I would recheck your keyboard (SD-1)settings and make sure that is set properly.
Next go into your software on the computer and check the port setting recommended by the software. Then try one port then the other.
Last but not least - Where did you buy your computer and if it was bult by a lcoal or amature they my have put the connecting cable on backward inside the computer (least likely senario) or even left them unconnected.
Jerry