Is this a brand new install? Is there a radio hooked to your sound card? I've run into this once where the COR pin was active high, thus disconnecting the DB25 caused it to think there was a signal on the input thus causing PTT. Are you using a DMK  URI? Are you getting ptt indication?

N1XBM
Apparare Scientor
Paratus Communicare
Allstar Node # 27086, 41540, 41812