Hidden Parts wont show up in assembly when I unhide them

[WM_13593280]

There are a bunch of hidden parts in my assembly I want to see but when I unhide them with the "show" button they don't show up. If I open up just the part by itself, it just opens up an empty part. I can see the outline of the part when I hover over it in the navigation tree but I can't find any way to enable it. Any help would be appreciated! 

I was sent this file so maybe it has something to do with the parts being on someone else's computer but half of them load so I don't really know why it's not working.

Below is a picture of the hidden parts and the outline I can see. Clicking suppress, activate, or show doesn't do anything.

This is what I see when I open the part. It only ever has the outline. (I made sure the display style isnt in wireframe)

[ArnoldCollett]

Is the part only a surface that's on a layer?

You might try to solidify the surface with a thickness.

[StephenW · Accepted solution]

I tend to agree with @ArnoldCollett . Do mass properties on the part and see if it has any volume or mass.

Layers may be turned off for surfaces. Usually imported surfaces look like solid models but lack volume and will disappear with surface/quilt layer turned off.

[WM_13593280]

Under mass properties says it has no mass like you said so I tried to solidify it but that didn't work. But you were right going into the layer tree everything was hidden. Showing them all brought everything back! Thanks for the help!

Step by step for anyone else with this problem. View/Layer Tree/Show

  

[SYNDAKIT]

I'm guessing the parts have an imported feature. 
Edit definition on the import and click the green check and it just may show up again. 

I see the second image is indeed an import