Connect your Fingerprint module with Arduino. Acquire data through Arduino. Accept a serial command from serial port in Arduino. If the command is equivalent to some code, enable the Fingerprint module.
You can check my following tutorial for PC+Arduino+Fingerprint module interface.
http://grasshoppernetwork.com/showthread.php?tid=652[
^]
I am not sure what Fingerprint module you have, so if it is R305 or similar, the above link might be helpful to you.