Which web browser and what kind of device are you using? I can't remember any major browsers or devices which can't load the tests, but maybe just which ever one you are using isn't able to?
Also, you might want to try turning off any browser extensions you've donwloaded, to see if it will work after doing that.
I'm using chrome on a pc, and I'm not sure what I did. I closed the tab and then reopened the webpage and it worked then? I'm not sure why that fixed it but simply refreshing the page did.