problem with slideshow backgrounds in windows 7 themes

[moltres_rider]

My backgrounds are set to change every 5 minutes but it won't change the background!!! I HAVE to change to a different theme then change back then it will cycle through the backgrounds but after a while the backgrounds will quit changing again and I am forced to do the same thing all over again!!! my background will only change for maybe the first 20 minutes then quit!!!