It sounds like the hard drive might have been going bad when you swapped it out. Maybe not. How is your Macbook pro working with the new drive? What was the other drive doing/acting? crashes? slow? any grinding noise?
Do you have any external cases to put the drive in. Like FW our USB. How much data is on the drive?
Do you know what TDM Target Disk Mode
is? This is often a good way to "grab data"
There should be ideas and some options. The less you mess with it until attempting data retrival the better. Trust me. I got in a hurry and killed a drive that was slowly working... but working.