The programming cable carries data, i.e. 0s and 1s, in serial form between your computer and your radio.
fldigi is looking for audio signals. You will need to find a way to connect your radio's speaker output and mic input to the sound card in your computer. You will also need to find a way to key the PTT in your radio. Sound card interfaces, such as the Tigertronics SignaLink USB, have what is essentially a VOX circuit that key the radio's PTT when sound energy is detected on the line going to the radios mic input. Tigertronics has a cable which should be compatible with your radio.