Start with an inventory
Write down what survives before trying to unlock anything: the old computer, the application version, the complete MultiBitHD folder, any external backup, the wallet words, and whether a hardware device was involved. Record what you know separately from what you remember approximately. A filename is a clue; it is not a complete diagnosis. Keep the original material unchanged and use copies for examination.
If you have the wallet words
Wallet words are a recovery route separate from remembering the application password. The historical restore documentation describes rebuilding a wallet from its words, while extra backup files can preserve notes and contacts. A correct-looking phrase is not enough to identify the original account: the wallet type and derived addresses still matter. Start with our wallet-types guide before choosing a derivation setting.
If you have a file but no password
First distinguish the primary encrypted wallet and rolling backups from encrypted ZIP backups. These do not all use the same protection mechanism. Record the exact filename, size and source device without uploading its contents. A password search needs both a compatible verifier and plausible candidate guesses. No finite search can establish that a password is unrecoverable unless its assumptions and coverage are explicitly defined.
If the wallet involved KeepKey or Trezor
Do not assume the desktop folder contains spendable private keys. The source defines hardware-backed and software wallet types separately. Preserve the device and its recovery information, and identify which type was actually created. The hardware-related source is historical; it does not establish compatibility with current firmware or current recovery applications.
What success should mean
A tool accepting a password, producing bytes, or showing a checksum is an intermediate result. A useful recovery should reproduce the expected wallet structure and previously known receiving addresses. Record which evidence supports that conclusion. Transaction activity and actual spending are later steps that require their own checks; this library never asks for a seed or signs a transaction.
A useful first message
Email mail@keychainx.io with the application/version, approximate creation date, backup types and exact error message. Say whether wallet words exist, without sending them. KeychainX operates this independent resource and offers commercial recovery services. Outcomes depend on the available evidence.