>>> Maybe Buenchico can help
Buenchico would like to but Buenchico is getting lost!
First, to clear up some confusion that seems to have arisen here, Codswallop is using a Chromebook, which uses the Chrome operating system instead of Windows. (I only know that because of his previous posts). Chrome OS is based upon Linux and, somewhat confusingly, uses the Chrome browser as the main route to access data and apps.
I'm familiar with the problem of data on hard drives (whether internal or external) not being fully visible when those drives are moved between different Windows computers. The solution there is for the user of the recipient computer to 'take ownership' of the hard drive. (It's fairly easy to do and just requires a few clicks of a mouse).
However I can't find anything online about 'taking ownership' of a drive within Chrome OS (or anything else that relates to Codswallop's problem), so I'm left stumped.
All I can suggest is borrowing a Windows machine, connecting both the external drive and a USB memory stick to it, then transferring the contents of the hard drive to the memory stick to see if the Chromebook will then be able to see them on that drive. (I suspect that it will. 'Ownership' problems only seem to occur with hard drives, not with memory sticks).
If the borrowed Windows machine also can't see everything that's on the external hard drive then these instructions should solve that problem. (They're written for Windows 7 but they will hopefully still work with other versions of Windows):
http://preyerplanning.com/take-ownership-of-entire-hard-drive-in-windows-7.pdf