Audio Systems: iPod, professional device, combination lock

Question
The person who is specialized in iPods are out on vacation, so I decided to ask you. I have an iPod, and once when I turned it on, I needed to enter a code, but I never put one on. There is a combination lock on the screen, and on the top, there is four boxes where I need to enter the code. I tried to press "menu", but I wasn't able to go back.

Answer
Emily - please, if you're an expert, enlighten me. I really don't care about the negative rating since I make a professional device that makes the iPod look like a toy and do very well with it. If you were able to unlock the unit, please let me know how you did it. I am 45 years in the electronic business and I don't know everything. I learn something everyday. That's why I volunteer my services free.