Test it with SeaTools for Windows: http://www.seagate.com/gb/en/support/downloads/item/seatools-win-master/
If the drive has failed the test will tell you. You cannot fix a failed drive, and the only way to get data off it is to send it to a data recovery specialist service which costs a lot of money.
You should have backed up the data to a second drive instead of relying on just one drive.