Junk Folder with circle/slash
 

I'm sure this has been answered somewhere in the 1000+ pages of this forum, but I just want to know why all of a sudden my junk mail folder has a circle with a slash through it and is not accepting any junk mail. Prior to this time, junk mail regularly was directed to this folder, and then one day I opened up Outlook and there was this orange circle and no junk mail. What did I do and how can I correct it? I have Outlook 2007.