Images in header stopped rotating...

I am not sure what happened but yesterday evening the images in my header were rotating just fine and now they have stopped.
I looked at the options under "NEW Header Images" and everything seems to be setup properly. I am not sure how to fix this. Could it be something to do with browsers? I am using both google chrome and safari and it was ok yesterday, so something is telling me that it is probably not the case.
Thanks for your help!