My Dell Inspiron laptop crashed a few weeks ago.
I managed to remove the 750GB SATA Hard disk from the laptop and i tried to recover the files from the hard disk by connecting it to another laptop via a SATA-to-USB cable.
However, when I accessed the hard disk, i can only see the RECOVERY drive. Why can't i see my files in the hard disk?
Appreciate if you could help to answer my question.
It sounds like the partition table or master boot record is damaged. Depending on how important the files are, you will need to weigh the cost of professional data recovery against the value of the data. This will cost in the high-$100s to $1000 at minimum - but if the data is worth that, it's the path to take. Anything you do to the drive yourself could reduce or eliminate the possibility of recovering the data.
During the Windows 10 upgrade on my inspiron 1532, I first observed that my documents had been moved to a windows.old directory; but following further attempts to upgrade, the directory appears to have been emptied. I'm wondering if the directory has become hidden or actually emptied, and I have to follow a professional recovery.
That's quite a different description than you posted above. Can you read the C: partition at all? Above it appears you could not. If you cannot, then data recovery is in order.
if you can, check the properties for the folder in question -- is it truly empty (0 bytes) or is there data in it?