I'm currently running a check disk on my external hard drive, and it's in phase 4 with no visible progress on the progress bar. Unfortunately, I have to turn off the computer that's running the test. Will shutting off/unplugging the hard drive prematurely cause the drive any harm?
Put your ear on the drive case and listen for a minute, if you hear no sounds of the read/write heads moving, unplug it, modern drives are very tolerant of unexpected shut downs regardless of when it happens, the only side effect could be corrupt data or an unbootable system drive.
If you hear a repetitious clicking at regular intervals, the drive may have suffered the click of death. Unplug it.