According to your video you were not using the board as it should. You can't have the USB cable connected without the power supply because it could damage the board. In order to use your boards you need to connect the power supply and then the USB cable. Take a look at the Getting Started Guide
In the FAQ ->
"Can I use this Intel® Galileo without a power supply?"
No. You must use a power supply at all times.
You could try to recover your board using the next processes:
ya i know, but usually, by accident, if I ever plugged out the dc cable there would be a red light by the usb port and as you can see in the video that doea not happen any more
Its not recognisable and it does not appear on device manager