|Three possibilities here:|
1) The hard drive is missing (check to make sure it isn't missing).
2) The hard drive itself may have failed (test it to find out, see below).
2) The hard drive is okay, but you need to buy a copy of Windows for it because it seems like someone has erased it.
First you need to test the drive just to make sure it's okay, otherwise you may be wasting your time trying to install Windows on it. You can test the hard drive with Seagate SeaTools for DOS which runs from a bootable CD: http://www.seagate.com/support/down...
To make the CD, use IMGBurn on any working computer with a CD-writer: http://www.filehippo.com/download_i...
Boot your laptop from that CD to test the drive.
If the hard drive passes the long/extended test, buy a copy of Windows for it.