If you rely solely on System Restore for your Windows backups, you're asking for trouble. Yes, the restore points created automatically by XP and Vista, and those I create myself, have saved my system from a failure on many occasions. But too often I've attempted to turn back the clock only to be informed that my computer could not be restored, or some similar error message.
Troubleshooting System Restore defeats the purpose, though it can be done; here are some instructions from Microsoft for doing so in Windows XP. If you use Vista, you've got much better backup tools at your disposal, so there's really no excuse for being caught without a backup in that OS (see more on Vista's backup utilities below). Here's a rundown on how to keep System Restore healthy in XP.
Don't expect miracles. System Restore won't protect your PC from viruses and other malware, and you may be restoring the viruses along with your system settings. It will guard against software conflicts and bad device driver updates. It doesn't affect data files in My Documents, Favorites, Cookies, and elsewhere, nor will it back up e-mail, or graphics files.
New accounts will be wiped out. If you created any new user accounts since the last restore point was set, they'll be erased, though any data files that user created will remain.
Newly installed software is only partially removed. System Restore deletes executable files and DLLs added after the restore point was created, but not the programs' shortcuts and other files. Uninstall the applications using Windows Add or Remove Programs in Control Panel prior to the restoration, and then reinstall it afterwards, if you wish.
Disabling System Restore wipes out your restore points. When you turn off System Restore, all existing restore points are lost. Also, you can't create a restore point while your system is in Safe Mode, so any restores performed in that mode cannot be undone.
Here are some ways to fix XP's System Restore:
Check your disk space: Right-click My Computer, choose Properties > System Restore, and move the slider left to reduce the amount of disk space reserved for restore points (thus reducing their total number), or right to add more space for more restore points. System Restore stops creating restore points when the amount of free space on the drive or partition falls below 50MB, and starts again when it reaches 200MB.
Avoid corrupt restore files: If your machine shuts down improperly while a restore point is being created, you may not be able to access that restore point. Likewise, making changes to a system file on a dual-boot machine can corrupt the restore point.
Peruse the event logs: Click Start > Run, type eventvwr.msc /s, and press Enter. Click System in the left pane, select the Sources tab in the right, and double-click entries with "sr" or "srservice" to view the description for hints at the source of the problem.
Nothing beats an image backup
As I mentioned above, if you use Windows Vista, there's no excuse for relying on System Restore for your system backup. And XP's built-in Backup utility is better than no backup, though it can't replace a disk-imaging program for reliability and convenience. If you haven't already, do yourself a favor and create an image backup of your hard drive.
In Vista, press the Windows key, type backup and restore center, and press Enter. Click Back up computer, choose a location for your backup (you can't store it on the same drive you're backing up), click Next, check the drives/partitions/devices you want to back up, click Next again, and then Start backup.
To use XP's clunkier backup utility, click Start > All Programs > Accessories > System Tools > Backup, and step through the wizard, or click Advanced Mode, then the Backup tab, and choose which drives and folders you wish to back up.
Note that restoring from this type of backup can be tedious, so consider investing in an image backup program, such as Acronis's $50 True Image Home (15-day free trial).
Tomorrow: supercharge your browser.