Android: Pictures, Videos, Songs, not showing up in gallery solution
The .nomedia file is what prevents or tells the android operating system to not show the media contents of the folder in the gallery. this file is sometimes created in the folder which has your photos, videos or music eg the DCIM folder.
Find and remove the .nomedia file
Go to the file manger of your device eg for samsung users go to my files app. tap on more and select show hidden files. now first look i all the folders which contain media files and you want the contents of that folder to be shown in gallery or music player. If any .nomedia file is present in those folders delete them and restart your device.
In most cases this will solve the problem. Note some time .nomedia file is present in your root(main) directory(folder) which prevent any media on the device to show up. So first find delete the .nomedia file from the root directory before going in other folders and doing the same and then restarting your device.
Media Scan Apps
If deleting the .nomedia file does not bear results the download one of the media scan/rescan apps available on google play store. open the app and do a scan on all the foldes on device and on your memory card of your device. wait for few minutes (1-2) and restart your device. This should solve the pics or media files not showing up.
The Media storage background process
Even after performing the above two process the media present on device is not showing up, the go to settings-->Applications-->Application Manager -->ALL. Find the process(app) named Media Storage, clear data and clear Cache. Then force stop the app.
Open your media scan/re-scan app do a scan. Wait for the scan to complete. And congrats you have all your media files present on the android device showing up in gallery and music player.