While I do not run Windows 7, I did have this same problem a while back with my two of my Windows XP (SP2) systems, as well as on my old Windows ME system. Each system had different problems/resolutions and I will give you each one that worked for me. Hopefully, there is something I will detail below that will also work for your Windows 7 system...
-=Resolution 1: The most likely culprit is that the System Restore folder has been corrupted somehow. Going on this assumption, do the following (note that you will lose any and all previous restore points you might still have by using this method)
a. Right-click My Computer> Properties, then click on the System Restore tab.
b. Check the box that says "Disable Restore on all drives"
c. Click "Apply" then reboot your PC. (you will be prompted to reboot)
d. After the system fully reboots, go back to the System Restore tab again and uncheck the "Disable Restore on all drives" box.
e. Reboot once more.
f. After the second reboot, go to Start > Accessories > System Tools > Restore and choose "Create a Restore Point"
g. Name the restore point whatever you wish (Date and time will be automatically added)
h. After the restore point has been created (assuming without error), go back to Start> Accessories> System Tools> Restore and choose "Restore my computer to an earlier date and time". Select the restore point you created.
If all goes well, you should receive a message that the system has been successfully restored.
-=Resolution 2: Assuming your system is in good health and that your have checked for viruses, spyware and disk errors, there are 2 other possible causes for your problem: