iMac version 10.8.5 keychain isn't working and I didn't send the backup keychain to Apple

view story

http://superuser.com – `How can we get into the computer without the usernames and passwords?What if there's an administration reset/backup keychain set and I can't remember what that is. I've tried every old password and the password hint isn't matching my answer (fantasy-place+year = Legoland80). Can I reset my computer completely? How do I go about doing that? How do I avoid that? I didn't send the key to apple like I should have, but took a screenshot with my computer, which is now not accessible anymore. I tried some other suggestions like deleting keychains, but I can delete all of them EXCEPT the one th (HowTos)