It could take you a few weeks to remember it. Heres what you do.

Continually write down every password you can ever remember.
Then think about things that happened during the time you bought it. I'd you still have internet search history on your PC from that time revisit all of those websites and read the stuff you were reading years ago all over again.

It can help jog your memory

I forgot a password before and did this for a few weeks and got it eventually