If you have gotten the I/O error during an operation…here is a fix that worked for me.
I took off the outer casing (Tabs surround it, just get a flathead in there and pop up) (I am out of waranty, so it makes sense) and then I got the hard drive out, disconnected the adapter, and slid the drive into my computer(Hot-swappable bays). After a restart it let me format it in Disk Managment(See other posts). And I am able to read/write to the drive.
Not recommened when you need data from the drive.
I also plugged the adapter in without the case; it didn’t work, so I think my adapter had a failure.
Hope this helps.