The hard drive may have failed. You can confirm by testing it with a bootable CD.
Download
SeaTools for DOS CD Image (it's an ISO file) from here: http://www.seagate.com/gb/en/support/downloads/item/seatools-dos-master/
Then install
ImgBurn on any working PC which can write to CD:
http://filehippo.com/download_imgburn
Use
ImgBurn to create a CD from the
SeaTools ISO file.
Boot your laptop from that CD and SeaTools will shortly open.
Select your laptop's hard drive and, from the menu, choose "Long/Extended Test".