Is my hard drive terminal?

I took the hard drive from my old mac laptop and put it in an external hard drive case. I managed to copy some files off it (onto my new mac) before getting an error msg and the case's icon disappearing from my desktop. I restarted my computer and plugged the external hard drive in again and got the msg "Disk unreadable - Do you want to initialize". What is broken - the hardware or the hard drive? If I buy another case will it work or would I be wasting my money? Should I be saying goodbye to my old hard drive and everything on it? :(