How do I recover access to my blogspot blog when it seems I have forgotten how to log in to the account?

I created a Blogspot blog in 2004, used it heavily for a few years but not these days, still, it’s a chunk of my life I do not want to lose and now Blogger have sent me an e-mail:

You are receiving this message because your email address is associated with an unmigrated legacy Blogger account. As we announced in April of last year, legacy accounts will no longer be accessible after May 30th, 2012 unless they are updated to the Google Account system. Any blog content associated with this account will also be unmodifiable after that date.

I’ve tried to sign in over and over again, changed my password but nothing seems to work… Help.…