I have already recovered the data. I just wanted to figure out what component was that. I'm not going to buy the new hard drive as now everything works fine but I can use only one HD at at time. If i need another HD I have to solder the part back.
I found that component. It is a transient voltage suppressor from ON semiconductors 1SMA5.0AT3 device code is QE which means that the working voltage is 5.0 volts. Hence, i've almost solved my problem

Glad you worked it out. This part has been discussed so much, I assumed you knew what it was. Search TVS to see what I mean

are you still in search of an ST3300622A 300GB HDD because I have one available but mine is 3.AAH Firmware and the site code is WU. IT works perfectly fine so let me know.