The original code you got with the unit will always override one that you entered. As long as you have the product card (in the information that came with the unit) you should be all right. If you lost that card you can try resetting the unit, but I think the code is designed to still be in effect. Let me know, I can do somemore digging..... Do you still have the owners manual (google it and you can download it free)
Jer