Hi Jay
Not sure what device you're using to view the site, but I find that when you click on an image it seems to shoot down and out of sight. So you could try scrolling down to see if it appears.
Alternatively you could open the image in a new window and then you should get it full screen. Right click on the mouse if on desktop or laptop, press and hold to get drop down menu if on phone or tablet. If this doesn't work, let me know and I'll have another think.
Wendy