It may have failed. You can test it with Hitachi diagnostic software called "Drive Fitness Test" which runs from a bootable floppy disk or CD: http://www.hgst.com/support/index-files/simpletech-legacy-downloads#DFT
To make a bootable CD containing the testing software, download the CD IMAGE
Make a CD from the ISO image file with "IMGBurn" from here: http://www.filehippo.com/download_imgburn/
Then boot your PC (the one with HDD problem) from that CD. The "Drive Fitness Test" will open automatically after a few minutes.