Hi there kathayes,
Unfortunately, this could indicate that there's something physically wrong with the drive. Can you attach it in some other way, so you can make sure it is not the connection that is causing this?
As for transferring the data, you have several options:
- Cloning the drive onto another one. This would clone everything. (whole drive and eventually some errors or corrupted data if any)
- Use some back up tool. (brand specific or a third party one)
- Manually transfer the most important data and try one of the previous options.
It may be a good idea to stop all the programs accessing the secondary drive. (if any)