Scanreg is Windows utility included in 98 and ME. Every time you successfully boot your computer, scanreg makes a copy of the Windows registry.
When to use scanreg: Scanreg is (most likely) a last ditch effort before reloading windows. Think of scanreg /restore as 'turning back the clock' on your Windows registry. Any programs or games that were installed between the date you turn the registry back to and now will need to be reinstalled.
How to use scanreg: Boot to a 98 bootdisk. At the a: prompt type c: then press enter. At the c: prompt type cd windows\command then press enter. Here you have a couple of choices. For our purposes here, we'll just stick to the basics. First type scanreg /fix that will attempt to repair the registry. Reboot the computer without the boot floppy and see if scanreg worked. Chances are....it didn't. If it didn't work reboot using the 98 boot floppy and start over.
Once you are back at the c: prompt type scanreg /restore you will have a choice of 5 dates to choose from. Pick any one you want, but keep in mind the further back you go, the more likely it is that you will have to reinstall programs or games. Once you have restored, reboot without the floppy.
If you still have a corrupt registry, go back and choose an earlier date.