Why can't I personalize my computer or change homepage?

I am having a problem with my computer. And now I am unable to change my background or screen saver settings on Control Panel. And I also can't change my home page or add my favorite websites. I am also receiving a message that my "user profile did not load correctly and if I make any changes, it will be lost when I log out. I have scanned my computer using "Microsoft Security Essentials" and "Windows Malicious Software Removal Tool", and there are no viruses.