Thanks for your help!
Put the text below in the BIP32 Derivation Path box.
m/0'/0
Type your password into the BIP39 Mnemonic box.
With password you mean the 12 wallet words?
The page should automatically generate your extended private key and a list of receiving addresses for your wallet.
How can I use my extended private key and a list of receiving addresses for my wallet to open my locked wallet? Can you explain this step-by-step? This is complicated stuff for me.... Do you have any idea why MultiBit can't open my wallet?