Time machine

I don't fully understand your problem because your request isn't that clear. I assume you do have a valid Time Machine back-up and when you talk about your C Drive you mean what my 2004 iMac's internal drive is called, Macintosh HD, and it's stuffed.

Mine blew-up and I fixed it by buying a USB hard-drive, not that expensive. Then:

Format New Macintosh HD

1. Unplug back-up disc (ensures it doesn’t get formatted in error).
2. Utilities (top line) > Disk Utility [using your install disc].
3. Select top part of disc name > Erase.
   1. Format: Mac OS Extended (Journaled).
   2. Name: Macintosh HD
4. Erase button > Erase.
5. Close down (top left Red button).
6. Plug-in back-up disc.

Then I did a full restore from Time Machine.

Please note, I'm not an expert here and your situation may be different, but, it worked for me.

Hope it works for you.

Hi again.

As it was late when I replied, I thought I would check it what I'd said this morning.

Reading it again, you said "everything seem to reinstall okay- he did check the back up status which was recent. The next step was to extract data from my back up". Where was the reinstall done from?

Was it Time Machine? If it was and your Time Machine disc isn't visible (mine was visible occasionally), then I suggest you do as I did, buy a new disc and do a back-up.

Now, here's the interesting thing. I wanted to retrieve some data from the 'old' disc and 'with fingers crossed' attempted it. It worked and has continued work every time I do an occasional back-up on it.

If your problem is the same, try leaving it un-plugged for a few days and then try again.

See mount section in 1st linked article.

Disk Unmount Using Terminal

Disk Utility – Force Mount Disk