First, the bad news: the longer you use Windows, the more it accumulates errors. Between the accumulation of user-installed program files ù many of which add to Windows' System Directory ù and applications that run in the background, conflicts get more numerous. Eventually it gets too unstable ù crashes or freezes occur more and more often ù and your only option is to wipe it out and start over from scratch. (I do this myself about once a year.)

The good news: you don't always have to reformat your hard drive in the process. Instead, you can usually wipe out and rebuild Windows while leaving your data ù and to some extent your apps ù intact.

A word of caution: don't attempt this procedure if you're in a hurry ù it will probably take all day. Here's what to do:

1. Gather what you need. This includes your Windows CD-ROM, as well as the CD-ROMs and floppies that your various programs and device drivers came on. Also, if your version of Windows is an upgrade, you'll need to have the discs for your earlier version of Windows handy.

2. Back up your Windows folder. Remember, you're not wiping out your hard drive, so copying files to another folder on the drive is a quick, convenient, and workable way to back them up. If you don't have room on your hard drive to make a full copy of the C:\Windows folder, copy as many of the important files as you can

3. Note important settings. Select Start-Settings-Control Panel. Launch any of the following applets that seem relevant to you, and write down their settings: Display, Internet, Modems, Network, and Password. How can you tell if something is relevant? Common sense. For instance, if you're the only person using your computer and it's not on a network, don't bother with Network or Password.

If you use a modem to access the Internet, select Start-Programs-Accessories-Dial-Up Networking. Right-click your dial-up connection and select Properties. Write down all the settings you see (or print the screen).

4. Prepare a bootable disk with CD-ROM support. If you have Windows 98, this task is simple: select Start-Settings-Control Panel. Double-click Add/Remove Programs. Click the Startup Disk tab, then the Create Disk button. Then follow the prompts.

If you have Windows 95, you will need a copy of your PC's DOS CD-ROM drivers on the Startup Disk, plus copies of autoexec.bat and config.sys with the command lines that call those drivers.

Before you go on to the next step ù the most unnerving ù test the new boot disk. Leave it in the drive, shut down Windows, and restart your PC. You should eventually get to an A:\> prompt. Insert your Windows CD-ROM, then enter the command dir d:, where d: is your CD-ROM drive letter, and press <Enter>. You should see a list of files and folders. Seeing this list means you can boot from the floppy and read a CD-ROM. You can now go on to step 5.

5. Wipe out your operating system. This is the scary part; it's not easy to turn back from here. At the A:\> prompt, type in these three commands, in order, pressing <Enter> after each one:

The last command may require several minutes to process. Take a break. When you come back, your computer will be unusable. You'll need to make it usable again.

6. Reinstall Windows. When the A:\> prompt returns, enter the command d:install, where d: is your CD-ROM drive letter; then press <Enter>. Follow the prompts.

7. Re-create your environment. Now you have to make the uncustomised, default version of Windows yours again. First, check to make sure the basics are working: Can the screen display your favourite resolution? Can you log on to the network? The Internet? If you have problems with any of these functions, re-enter the settings you copied in step 3, as needed.

Now restore the most important files and folders you backed up in step 2. If you backed up your entire Windows folder, do not restore it all ù the point of this hassle is to get rid of the accumulated garbage. But keep the backup around for a couple of months in case you need to restore a given file.

8. Get your applications working. This is the longest and the hardest part of the job. Right-click Start and select Explore. Test each program by launching it. Although the programs are still on your hard drive, some of them will not launch without pieces that were in the Windows folder before you deleted it. If a program fails to launch, reinstall it ù and be sure to put it in the same folder that it was in before.

9. Update everything. Every program you've reinstalled, including Windows, has lost any updates you downloaded from vendor sites. Use the programs' update features or visit Web sites to update the software again. Start with your antivirus program.