What is usual about this statement? "My friend asked whether I would try to save his PC. It kept on freezing and crashing, usual stuff."
Surely it is not usual for the system to keep freezing etc. The problem could be many, hard drive may have in fact died but have you checked out the power supply? Bad ram can make a pc freeze and if there is a hardware problem then trying to change the software (OS) will not help. Was there any warnings at all such as beeps on boot up (or just before (post)). Check the mainboard is not earthing and causing it to short out. It would also be helpful to know what the system is and how old etc. More spec = more chance