.key extension was most commonly used with Multibit. If you were to open the wallet file with a text editor, are there any human readable parts? It should contains some references to Bitcoin addresses, they're around 34 characters long and starts with 1.
i opened it with notepad, it a well strucktured block of text, but no adresses. might be encrypted, is there anyway i can use this .KEY with Multibit and Bruteforce it using my GPU farm ?