Pictures and videos disappear from my gallery after connecting via USB All my picture and videos (whatsapp and DCIM) are gone from my gallery after connecting my phone (Samsung Note Edge) to my computer via USB cable and till now I cannot retrieve them.

All my pictures and video still exist in my phone but you need to access them through my phone files (My Files folder).
Check if you have a hidden file named .nomedia (double check also for uppercase name) on device memory (storage folder) and delete.

Go to Settings -> Apps -> ALL -> Media Storage. Select Clear data + Clear defaults. Disable the App.

Reboot the device. Now enable again Settings -> Apps -> ALL -> Media Storage. 

Wait a couple of minutes (so it should reindex files). I think all files should be now again in Gallery. Note: Do not try to run any rescan App, just follow the above steps.

Source: Images have disappeared from gallery, but still in &quot;My Files&quot; (Samsung Galaxy S6 Edge, 5.0.2)