photo stream not enabled

I have tried to enable photo stream on my PC running Windows 7, but everytime I return to the photo stream folder on the Pc, no pictures are availalbe and I get a message saying "Photo Stream is not Enabled" "Sign in to Icloud to view Photo Stream."

I am signed into Icloud and my calendars are synching. Every time I open the iCloud control panel the Photo Stream radio button is unchecked. I then select Photo Stream again and hit apply, but nothing happens.

Any ideas or help?

Thanks