Is it a notebook or a desktop pc? If it's a notebook, you should just get an external USB drive, and not trying to open and check inside.
If its a desktop pc, first check if the cables (power and data) are still connected. If yes, you could: a) buy a new one (internal) and see if that works b) get the drive carefully out and check at another computer c) just buy an external USB drive and forget about the built-in one