There are a few reasons for this problem
SYSTEM RESTORE What to do if you have no restore points [Tutorial]
If you do not have any restore points on your Windows Vista or 7 computer, it may be because Windows is not creating restore points automatically. There are a few different issues that can cause this.
One cause is a lack of enough free space on your hard drive to store the System Restore files. To fix this problem, make sure you have at least 300 MB of free space on your hard drive (50 MB if your hard drive is smaller than 300 MB and you are running Windows 7).
Another cause of missing restore points is a problem with the task scheduler. Before you begin troubleshooting this problem, click the Start button and type Services.msc in the Start Search box. Check to see if Volume Shadow Services is running.