Please someone help me, I want to save all my video files on an external hard disk for back up reason, my problem is this i have some video files that can play on my internal hard disk but can't play on my external ? why it so? first i thought that the file (on my external hard disk ) is corrupt but when i copy back to my internal hard disk it play without any problem.

Maybe the file is not finish copying when you unplug your portable drive (just an idea).

When copying files, much better to select it then press CTRL+C or right click mouse copy then paste it to destination drive. Rathen than drag and drop files. Dragging & dropping files sometimes only create shortcuts instead of copying it.

Also, make it a habit plugging huge size storage devices (like your portable) to the USB port at back of CPU. Not in front. This will save your portable from damage.

then it would be damaged and also not readable after copy back to pc