I started up in Safe Mode and was able to Defrag (through System Tools), but no such luck with the Scan Disk utility.

It took about an hour to work through approx. 200,000 of more than 2 million "clusters," during which time it stopped and restarted repeatedly. After 10 restarts a message popped up saying that it was happening because other Windows programs were running, and did I want to continue? I replied yes, it kept at it, then a short while later I got an error message (a general protection fault, I think) and that was as far as it would go.

I thought that Safe Mode was a "bare bones" version of Windows with little or nothing going on in the background, but clearly something's happening on my system that's preventing Scan Disk from working properly.

Any ideas what that might be? THANK YOU!

Sounds like you have scandisk set to the thorough scan and not the standard. That is why it is checking clusters and taking a long time.

Safe mode IS bare bones. Explorer is the only thing loading. If you are truly in Safe Mode it will say so in all 4 corners and look bad (16 color mode). Tap F8 or hold down the LEFT CTRL key on startup then select Safe Mode from the startup list.

Yes, it was definitely in Safe Mode.

And yes, it was running a thorough scan, not a standard one. Is thorough unnecessary?

How does that sort of scan compare to the Norton one that's set to run once a week on my PC? I thought they were different (scan disk for system & file problems, Norton for viruses) but there's so much I don't know, it's scary. I don't know where to begin!

You can do a full Scandisk in DOS its quicker that Windows. Just start your comp up whilst holding down the Ctrl key and choose Command Prompt Only from the menu.

Just type Scandisk.

The complete, or thorough scan, not only checks for software errors, but also checks each sector on your hard drive for physical problems. This read/write process as you have found out takes a very long time, especially if your hard drive is over 20 Gigs, and there are better applications out there that will do this in less time.
Use scandisk in regular mode, and be sure you check the option to "fix all errors found."

Regards,
John