External HD Problem ?

Hello,

Have a Seagate Free Agent external 750 GB HD. About 3 years old.
About 735 GB used.
Usually kept unpowered.
Last used and plugged in about 6 months ago.

When I look at it now, all the Folders and documents on the screen
that opens look perfectly normal. Everything that I remember as being there apparently is showing.

But-

That's about as far as I can get.
Clicking on anything (a Folder or a document, e.g.) does nothing.
Nor can I drag, or Copy, a file or document anywhere.

Tried recycling the USB cable,and the power cable, but that didn't do anything.

No error msgs. although my son playing around with it last night
says he did get an I/O error msg.

Sometimes, but not all the time, there is a green horizontal bar
that slowly fills up over about 20 seconds; as if it were copying, or completing some other function.

I would think that the HD has just conked out totally, except that everything opens up as it should when the drive is accessed.
Just can't go from there.

Any thoughts as to what to try would be most appreciated.

Thanks,
Bob

Let us have a look at how your Seagate external looks in the Disk Management. Please upload the screenshot.