Question for you:
Are you running a third-party defragmentation program ?
Sometimes these types of programs can interfere with the creation and/or delete the Volume Shadow Copies created by System Restore.
For instance, Diskeeper has a Volume Shadow Service (VSS) Compatible Mode defrag, which needs to be turned on.
Speaking of which - you should check to ensure that the "Volume Shadow Copy" service on your computer is enabled and set to run on Manual. System restore relies on this service.
You can also create a task in Task Manager to automatically create a restore point at the times you desire.
You can find the step-by-step procedure, along with the script which you can download and run yourself, in the following tutorial from Windows Seven Forums:
"How to Create System Restore Points with a Restart or Windows Task Scheduler"
Hope some of this is helpful.