I have my windows 7 (Home Professional if it matters) set to automatically change the background every 20 minutes with the source of the slideshow as a folder in the Pictures library. Recently, the slideshow has not been functioning. The pictures do not change while the computer is on; they only seem to change when it is shut down (i.e. there is a different desktop on each boot), or about 50% of the time when waking the computer from hibernation. I've changed the time settings, the folder location on the drive, and made sure to disable all programs that tweak the desktop with no luck.

Any thoughts?