There are a series of check you can do in order to diagnose the issues your self before you contact a professional to fix your possible hard drive failure. 

1. The first thing to check is to see if you are getting power to your device. Power failure can be a result of have a bad USB connection, bad USB cable or the connections inside the hard drive caddie is come apart and not connecting from the main power board to the hard drive inside. 

2. Put your ear to the hard drive or hand over the hard drive. If you feel its still vibrating a little then you can eliminate the power failure. If its not spinning then you can determine that their is a complete power failure or your hard drive has failed. 

3. Your hard drive still turns on, its spinning but when you connect it to your computer or laptop is fails to show in your system. This issue is more so a logical error and could be your firmware causing the issues. 

4. Clicking hard drive, this means that your headers have been nocked out of place and require replacing. You have to be sure to not turn on the hard drive is you hear clicking sounds. If the headers scratch the platters of the hard drive your data can or will get damaged and your recovery chances become significantly lower. 

In general, when data recovery is required their is a process, this is where we take the hard drive offsite into our clean lab and open the hard drive and perform a series of tests. We check the firmware condition and the internals to determine what the issues are. Many customers are unaware of the process and have to understand that it has to be done this way. 

One we have found the issue when then issue out customer a report on what we found. The customer then has the right to choose to go ahead with the repair or not. 

I hope you get a better idea of what data recovery process is all about.