Last week I fingered Vista Disk Defragmenter for running at inappropriate times (namely, while I was working) and slowing my system to a crawl in the process.

What I neglected to do, as a few alert readers informed me, was explain just how to turn off Disk Defragmenter, to stop it from running whenever it pleases.

My bad--I shouldn't have assumed everyone knew how to do this. Fortunately, it's extremely easy:

1.Click the Start button.
2. Type Disk Defragmenter and press Enter.
3. Clear the check box marked Run on a schedule (recommended).
4. Click OK.

As I noted last week, Disk Defragmenter serves an important purpose: to keep your hard drive running at peak efficiency. So if you do decide to pull the plug, make sure to run the tool manually from time to time, or replace it with a third-party defragger like Defraggler or one of the other tools from PC World Downloads.

Shut Down a Stubborn XP System

Reader Doug wrote to tell me of this problem with his Windows XP machine:

"When I attempt to turn off my computer, it will not power down all the way. Instead, it goes to the Windows XP logo that says, 'It is now safe to turn off computer.' Other PCs, including my wife's, turn off altogether. How do I eliminate this extra step?"

You didn't tell me the age of your machine, but I'm betting it's an older model. For starters, the next time you boot your system, hop into the BIOS settings and look for something called (or related to) Advanced Power Management. It needs to be enabled.

That step alone may solve your problem. If not, try this:

1. Click Start, Control Panel, Power Options. (If you don't see Power Options, click Switch to Classic View.)
2. Click the APM tab. (Don't have one? See below.)
3. Select Enable Advanced Power Management Support.
4. Click OK.

Now try to turn off your PC. If that didn't do the trick, you need to verify that your PC is ACPI-compliant (meaning it supports Advanced Configuration and Power Interface standards), and/or look for wayward device drivers that might be messing with the shutdown sequence.

Microsoft has a detailed support page devoted to this issue; one of these remedies should resolve your problem.

Solve Common PC Problems with Microsoft 'Fix Its'

Microsoft's Knowledge Base is a treasure trove of helpful information regarding common hardware and software problems.

Okay, maybe not a "treasure trove," and I wouldn't say all the information is "helpful." To put it another way, Microsoft's Knowledge Base is a frequently frustrating and only sporadically useful resource.