I would assume you've installed a new mIRC on a new computer/OS, so mIRC doesn't realise you've registered. You should have saved the email with your registration info, but if you didn't, check out the lost registration
page and have the info resent.
If you can't use those forms for whatever reason, all registration queries need to be sent to Khaled, [email]firstname.lastname@example.org.[/email]
Hope that helps!