Photos not displaying in preview after upload

After successfully uploading photos to a gallery (a new page) and saving the changes, I select the formatting I want from the ‘Gallery’ options; like linking the thumbnails to the images; the number of columns and ascending order.
The thumbnails are all clickable as they should be to change titles and so on and everything is exactly as it is in the YouTube video I’m watching which details the process. Everything works fine until I hit ‘Preview’. When the post opens, NO PHOTOS. I tried clearing my cache and rebooting. Same result. Any suggestions welcome. I’m using Win XP with Firefox, no ad block and pop ups allowed for WP.