As so many people commented on my post about my apparently failing hard drive I thought I'd post an update. Dell had me run some diagnostics that are on a special diagnostic partition. I ran the entire set of hard disk diagnostics which took most of the day including a full surface scan and the drive passed all tests without a single error. Therefore as far as Dell is concerned there is nothing wrong with the hard drive. It's possible that as Steve GW7AAV commented the operating system has marked the bad sectors so they won't be used any more, in which case hopefully the issue was just a one-off.
Active@ Hard Disk Monitor Free which seemed to display an impressive amount of information. This program said the Health Status of my hard drive was OK, though the value was only 55% which didn't seem too healthy to me. It's up to 57% now, which makes me think that something bad did happen and the value will slowly improve with continued error-free operation. A look at other screenshots of the program showed values in the high 60s so perhaps I shouldn't expect to see close to 100%. Hopefully if the problem occurs again this program will provide more information about what actually happened.
Annoyingly, when I started the computer the next day and looked at the stats I saw that Active@ Hard Disk Monitor Free is not free at all. It is a 14-day trial version. When I checked download.com I saw there were a lot of complaints about this. The old version was free, but not the current version. However it is only $6.99 to purchase a license for one PC so rather than waste more time trying to find another free alternative I have decided to pay for it.