problem with video gallery thumbnails

When i’m in the wordpress admin page and updating my video gallery, it will not allow me to change the thumbnail image. I click on the default picture like the Gridkit documentation says, then a white box pops on the middle of the screen and in the thumbnail section I select CUSTOM. The white box does not disappear, but the wordpress media gallery pops up behind it. I click on OK below the default selected thumbnail and it goes to an all white webpage. Basically wordpress bricks. What should I do?

disclosure: I’m not a website builder, just a regular gut trying to figure this out

The page I need help with: [log in to see the link]