So you did use the acccount you used in the first place to install 2142 for the first time? Did you buy the EA Downloader or the DVD version?
You should try to login with your original account, otherwise you'll need to contact EA, explain to them in very clear terms and mention it multiple times you have the DVD the manual, the receipt and the case and are willing to send it to them or make a picture of it, and they will most likely either send you a new key, ask for the number on the DVD (its written in small lettters, dont give it to anyone but EA support!) and give you a new key or will ask you to send the entire package plus 5$ to them.