My External Hard disk is not working all of a sudden and it is not shown in disk management too.
It might be trying to use the same letter as 1 that is already thereif u know what I mean if u open up my computer u have like c: D: E: F: ETC
Is that USB drive? If so download USBDVIEW and run that as admin. Look for the disconnections and remove all of those. Make sure you remove all USB devices except those connected like keyboard, mouse, WiFi. Once you remove disconnections reboot the system. Don't connect anything until the system is rebooted. Once reboot then add your USB devices to the system.