I assume your "aprs software" is APRSIS32?  Are you running development version or general release?  What does it say in your About box?

What is your GPS?  Is it directly connected to your PC or running through an APRS radio or TNC?  Are you sure it is NMEA?  Does it come through a COM port?  Have you connected a terminal emulator to said COM port to see if you get readable NMEA strings?

So many questions, and probably more to follow!