Note: For best results, you should run System Restore from safe mode.
If you receive an error while restoring, then use it from safe mode and it should work fine. To get into Safe mode, you can reboot and use the F8 key right before Windows starts up.
But even better is from within recovery environment.
Maybe some virus/malware or antivirusscanner is blocking the system restore now? In recovery environment run a special small windows version so no interference of trouble-software