Excel 2013

While working in excel 2013, I somehow locked the entire workbook and now cannot enter any data in any cell. My data is there, but I can't add any new data. I've tried following the help files for unlocking the cells and even the whole sheet, but nothing works. I don't know what I did, or how to fix it. I have over 5,000 lines of data, and it will take weeks to re-enter everything. What did I do, and how do I fix it? Please help!!! - Rick Iaccino