Finding Old Bitcoin Wallet
By Wallet key, do you mean private key ? If you have private key, you can use any bitcoin wallet to import the private key https://en.bitcoin.it/wiki/How_to_import_private_keys

A common bitcoin private key looks like this:

5Kb8kLf9zgWQnogidDA76MzPL6TsZZY36hWXMssSzNydYXYB9KF


If your key doesn't look like this, its probably a password for the bitcoin service where you created the wallet. You need to locate that service and login into it with Wallet Name/Key to get to those bitcoins.