Hard disk problem

Hello,

I have an inspiron. Recently, the laptop cannot be booted.  It failed auto-diagnosis. And it showed hard disk error. Since i did not have a back up, how to restore or copy all files to USB is the most important thing. I tried to take the hard disk out and put it to another computer.  It required an encryption key. I wonder when my hard disk is encrypted. I know nothing about encryption key.  Could you please help me out to see how i get get all files from that poor hard disk please? many thanks