ok i understand now. 
no, when you format, i believe your cd key information will be
permanently lost.
however, for companies with good support, the best way to recover
your cd-key would be to login into the company website for any
cdkey recovery solution. some sites like microsoft.com do provide
cdkey recovery support in case of situations like yours. i'm unsure
about nero, though.
of course, this can only work if you have registered with nero
before during your installation process. otherwise, there's no
other way than to look for your cd cover again. 