Turning the drive on and off is the worst thing you can do as it has probably corrupted your data.
As mhansen1 says, do not format the drive. If you want to disconnect the drive you should be able to open Windows Explorer and right-click the drive icon before choosing Eject, after which you can unplug it safely.
Failing that, shut your computer down, and then disconnect the drive.
Looking at your internal drives, I'm a bit concerned that they are full with very little free space and I'm wondering if that has some bearing on your problem.