Hello Karen Richards,
The first step you should take is to examine the S.M.A.R.T. logs of the disk to see if there are any logged issues. You can do so by downloading HD Tune pro and trialing their software to read the S.M.A.R.T. logs. Once the program is installed you can select the disk in question from the drop-down menu, then click on the tab that has the red + indicating Disk health and this will list S.M.A.R.T. data.
If you see anything in the list in red or yellow that will be the disk letting you know what is failing, weather it is CRC errors or failing or bad sectors.
If there are no recorded errors then you might be able to recover your disk yourself.
If you tap or click here you can find a list of steps to take if there are no logged issues with your Hard Disk Drive.
If you care about this data and absolutely cannot lose any data on this disk, you definitely want to send it in for professional data recovery.
For professional data recovery, I recommend Gillware – https://www.gillware.com/