Otherwise, you can check the following locations on old computers (and your current computer):
- Email inbox for emails from blockchain.info if you had one of their web wallets
- ~/.bitcoin (or user profile/appdata/roaming/bitcoin on Windows) for a bitcoin core wallet
- ~/.electrum (or user profile/appdata/roaming/electrum/wallets on Windows) for an Electrum wallet
- MultiBit folder in your home folder (or appdata/roaming/MultiBit or Multibit Classic) for a Multibit wallet
Additionally, if you think you might have had a "brain wallet", you can use https://brainwallet.io (download and copy to an offline computer if you're paranoid) to try old passwords you might have used, possibly using the "generic" option. Under no circumstances should you create and use new addresses using this tool, or continue to use old addresses made with it.