See this Microsoft article: How to use System Restore to Undo Changes if Problems Occur

If there are no System Restore points for you to restore to, check the following:

1. If the Task Scheduler service is disabled, System Restore won't create restore points. To check it, click Start then Run, type services.msc and click OK. Scroll down to Task Scheduler in the left (Name) column. If the service status isn't Started, double click on it to open it's Properties window. Set the Startup Type to Automatic, then click on the Start button to start the Task Scheduler service, then close the Properties window.
2. Low free disk space can also prevent System Restore from creating new restore points. The service needs 1 to 2 GB free on the partition where Windows is installed in order to make restore points. If it doesn't have that, free up some space by following directions here: Clean up your hard drive to increase free space

This post has been edited by Ztruker: Apr 7 2009, 06:45 PM