Alot of the time, when your hard drive is running out of disk space, System Restore will not only stop monitoring to create restore points, but delete them to save disk space.
You can also check log files to see what event errors occurred.
Try this:
1. Go to Start > Control Panel > Computer Management > Event Viewer > System.
2. Click on the Source tab to sort by its name.
3. Go to View > Filter and next to Event source, select srservice, and press Ok.
Were you able to find System Restore in here ok? If so, what errors do the event logs in the description report?
Gizmo73