It is possible that the hard disk may be faulty or it could be a random read error due to corrupt system files. In terms of faultiness, it could be something very serious or a minor problem like a bad sector. Bad sectors can be marked and ignored although it’s usually better to replace the drive just in case.
You may also want to burn and run the below ISO to check the disk (assuming it’s a Hitachi one and not Toshiba):
http://www.hitachigst.com/downloads/dft373_25.iso
I actually believe the test can check Toshiba disks as well but you’re more limited with what you can do with it and you get no support..however it’s worth a try to check the surface.
You could also just restore the system using the CDs and see if that solves the problem as well.