I assume you have a DSC PC1555, since I don't know of any other panel with that number.
Two questions:
(1) Do you have your Installer Code? This is a different code from your Master or User's Code. It's not impossible to program without it, but it's a major undertaking. You would have to default your system and program everything from scratch, which would entail figuring out how your system is currently programmed in the first place. If you don't have your Installer Code, you might be able to get it from the installing dealer.
(2) Do you have and LCD keypad (that displays words), or just an LED keypad (that displays only LED indicators)? Either will work, but the programming instructions are different.