Screensaver Won't Turn Off

I have a Windows Vista PC (Lenovo Thinkpad r61) that is acting buggy. It won't let me turn off the screensaver. I go into the screensaver settings, set it to 'none', and then click 'apply' and 'ok'. When I open the screensaver settings again, though, nothing has changed. I went in and found the 'ScreenSaverActive' key in the Registry, and tried to change that from 1 to 0, but it won't let me. I'm the administrator on the PC.

Help?