Close down the MiniCDU program. Can you unplug the device and plug it in with the provided cable to a different USB Port? Then, go to your Device Manager to check the com port. You can do this by pressing the Start (Windows). Right-click on Computer > Manage > Computer Management > System Tools > Device Manager > Ports (COM & LPT) > Prolific to USB Serial Comm Port (COMXX).
Open up the said program and press the Connect button. Go to Mode > Setup COM Port. Select the com port and baud rate and click the OK button. Now, press the Connect button and you will see some scrolling data on the Terminal window. Also, you'll see some data in the blank fields. Check the Terminal window to see if you're getting the proper NMEA data.
Let us know how it goes.