Are you photos/video clips on Track 1 - the uppermost track? If not, they won't show up in Storyboard mode.
Why would you switch to Storyboard mode if you've started in Timeline mode? Normally, one would start in Storyboard mode then switch to Timeline mode to do more detailed editing.
So it would appear I am having this same issue. How do I move all of my photos/video clips to the uppermost track? (Not sure how I moved them to track 3).
To move all your photos/video etc. from track 3 to track 1:
Hold down the Shift key and click on the first and then the last objects in the track. All should now be highlighted.
Release the Shift key and hold down the Ctrl key.
Click on any object in track 3 and drag it to track 1. All the other objects should move with it. Release the Ctrl key.
Make sure the first object is right at the beginning of track 1 (it is easy to actually move everything to a later point if you're not careful). You may need to hold down the Shift key again at this stage to ensure that ALL the objects move together.