Thank you, Cas.
I should mention that although there's a Windows version of smartmontools, I don't think its very easy to use, due to its Linux origins. I only suggested it because I'm hesitant to recommend something I haven't used myself, and I have used smartmontools on Linux. There are other Windows-specific tools which you can find by googling "windows smart disk monitor". (If I wanted to check out the hard disk on a Windows PC myself, I would do it using a Linux "live" (bootable) CD, since that will work even if the PC can't be booted from its hard disk.)