Re: cannot access [dir]: Input/output error
Input/Output Error is a horrible error. It usually means that part of your disk is unreadable or unwritable - it seems like it's unreadable in your case. Unreadable parts of the disk are very bad indeed as they often mean that you've lost whatever data was in that part.
You could try FSCK, which stands for FileSystem ChecK. Unmount your disk and run the 'sudo fdisk -l' command to work out the device name of the disk (it'll be something like "/dev/sdf"). Then put it into the following command:
With luck, the immediate problem will be fixed, at which point you should back up your data straight away and throw away the faulty disk.
I try to treat the cause, not the symptom. I avoid the terminal in instructions, unless it's easier or necessary. My instructions will work within the Ubuntu system, instead of breaking or subverting it. Those are the three guarantees to the helpee.