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How do I fix System Restore? My old restore points vanished, and Windows won't create new ones.

George Vipond, White Rock, British Columbia

System restore should back up the Registry and many important system files frequently and automatically in Windows XP and Vista. But various conditions can prevent System Restore from creating backups or (as it calls them) restore points:

Tight drive space: To create a restore point, you need about 200MB of free space on the system drive or partition (usually the C: drive). When this space is unavailable, your PC may stop creating restore points and may delete existing ones.

No Task Scheduler: System Restore uses Windows' Task Scheduler to create system restore points automatically every day. To make sure Task Scheduler is active, select Start, Run (or Start in Vista), type services.msc, and press Enter. Scroll to and right-click Task Scheduler, and choose Properties. If 'Service status' isn't set at 'Started', click the Start button. And make sure that 'Startup type' reads 'Automatic' before you click OK.

No rest for the OS: System Restore creates restore points automatically only when your PC is turned on but idle. If the system is always off, hibernating, or in use, you get no automatic restore points.

Even when System Restore works properly, not all restore points are usable. Restore points aren't complete backups. Each holds only the changes since the previous restore point, and System Restore may need to use all the restore points on your hard drive so as to revert to any one of them. In that case, if one restore point is corrupted, they're all useless.

If you can't get any of your restore points to work, remove all of them so you can start over; to do this, turn System Restore off and then on again. In Windows XP, select Start, Run, type sysdm.cpl, and press Enter. Click the System Restore tab in the System Properties dialog box, check Turn off System Restore, click Apply, uncheck Turn off System Restore, and click OK. In Vista, click Start, type sysdm.cpl, and press Enter (or select System Restore from the list of programs that appears as you type). Click the System Protection tab (or choose open System Protection), and uncheck Local Disk (C:). The exact name of this option varies, but it should end with '(System)'. You may have to wait a few seconds for it to appear. Select Turn System Restore Off in the System Protection pop-up, click Apply, recheck Local Disk (C:), and click OK.