Sound like the hard drive may be failing, if not actually failed. If you need to rescue any data from it, remove it and install it into another PC as a second drive so you can copy data from it and save it somewhere else.
Then test that drive while it's installed as a second drive. You can test it with SeaTools for Windows which obviously you'll need to install on the host computer: http://www.seagate.com/gb/en/support/downloads/item/seatools-win-master/
Strongly advise you rescue data from it before
you test it.