I Need Help To Get Into My Facebook

I Entered A Fake birthday at the time of applying for the Facebook, and I don't remember it now. I was worrying that people might know my birthday. And that is why I entered the fake birthday, and I don't remember what is the date. Because I upgrade my lap top from Window 7 to Window 8, then I got the messages saying it is from a different device. I must enter my birthday that I don't remember. Please help me to get into my facebook again. It is important that I have a lot of friends there that I want to connect with them again. Many, many thanks. Linda