Following a recent power cut, my computer is now no longer reading Drive F of my external hard drive. This drive did contain 28 years worth of material which is invaluable and irreplaceable but is now saying that it needs to be formatted. I am at a loss as to what to do. I have gone into the Management section and it says that the drive is healthy and active but has 17.76 GB of free space and nothing written on it. Can anyone help me retrieve any of my data?
Do NOT format the drive - but you knew this, anyway.
First step is what fihart said - try it as an internal drive, in case the problem is entirely in the external case's power supply or interface electronics. That may be a total solution for your data recovery. Then your task would be reduced to a relatively simple one of buying a different external case and mounting the drive in it.
But, if the drive still behaves the same way when mounted as an internal, then you could have one (or both) of two problems: corrupted info in the Partition structures, or corrupted data in the files (most likely in the directory and tracking files) within the Partition itself. For each situation you can get either Partition Recovery or Data Recovery software - some free, some you pay for, but the best ones are NOT free, unfortunately.
For a good place to start, try looking up GetDataBack NTFS. It is considered mainly a data recovery package and it is NOT free. But it has a very useful "free trial" system. You go to their website and run the Free Trial version. It will completely analyze your disk and show you in detail exactly what the disk will look like (with most or all the data files recovered) IF it were to do the job for you. If you are satisfied that the tool does everything and you like their price, you pay them right then and the job is done on the spot. You now have all your data back and a downloaded copy, fully licensed, of the software to use again. If you don't like the projected result, you don't pay and just back out of the software, and it does absolutely nothing to your disk. Then you go looking for other tools.