I can't tell you how to get your old restore points back because they may be corrupt, but I can tell you how to fix this problem so you can get them in the future.
Right click My Computer, choose "Properties" then click on "System Restore" tab.
Put a check in the box for "Disable Restore on all drives". Click OK, then Reboot your PC.
After you reboot, go back to the System Restore tab and uncheck the box. Click OK.
Next, go to Start/Programs/Accessories/System Tools then click "System Restore". Choose "Create a Restore Point" and give it a name like "Reset" as a reminder.
Try to restore using the new point and it should work properly.