Images not loading on WP2011

Hi after using the WP 2011 for a few years, noticed that in the last few days my images are no longer there not even the header. So, had a look around, couldn’t see anything wrong. Tried uploading them again and although it says they upload and the link appears in the media library can not see any of the images.
Any ideas? Your guidance will be much appreciated.
I have put the site on maintenance until I can sort the problem out.