Could be a number of things:
1. Parallel is disabled in CMOS
2. Device Manager has an error with Parallel Port
3. Your Printer Drivers are corrupt, or partially loaded
4. You have a Virus/Trojan
5. The Printer is off, or has malfunctioned
6. The Parallel cord or computer connection is faulty
Also what is the name and model number of your Printer?
What OS are you running?
And have you thought of updating to a newer USB? (they've been around for years now!)