Header problem

Hi
The headers on my pages have stopped showing up on my site.
When I go to the slider sets
snookerhmpg poolhmpg etc it shows my jpegs I was using,

I tried to upload the jpeg eg on my snooker page under a different name with no luck,
so I tried to upload the same picture within the site underneath the header and the new name ….snookerpic.jpeg veiws fine.
but when I upload the same url from that jpeg into the slderset
it comes up x.

I have tried copying the url from my lbrary file into the sliderset
url but still no luck.