I've been drag-and-dropping files between two open directories on two of my hard drives. It moves the file and removes the original from the original location.
All of a sudden, this doesn't work. Sometimes the file doesn't move/copy at all. Then when it does actually copy to the new location, the original doesn't get deleted.
For the life of me I can't figure out what happened or how to fix this? I've checked for updates, rebooted, etc.
You may already know this, but you didn't mention it. If the source and destination are different drives, it will copy by default. If they are the same drive, it will move by default. Also, by default, if you:
hold SHIFT while dropping, you will move (or SHIFT) the file from the source to the destination
hold CTRL while dropping, you will copy (C for CTRL = C for Copy) the file from the source to the destination
...regardless of whether the source and destination are on the same drive or not.
Note this same trick will work in more places that you probably realize. For example, in Word, you can select text and drag it to a new location. But if you hold CTRL while dropping it, it will copy that same text (leaving the original).
And, finally, if you're into mouse control, you can use the right-click to drag and drop. This will give you a small menu asking if you want to copy or move, as shown below: