And they will want to change anything themselves. While I consider this as [b]Unprofessional Conduct[/b] it does have the advantage of requiring you to return the computer to them for any changes that are made and guarantees them a sure income in the future.
But any IT Pro should know how to bypass this and do the proper Tests that are required to do any proper Diagnostic Work. But as the unit has been made this way perhaps you could ask the Makers Tech Support for a HDD testing Tool that they recommend or can be run within Windows. If they make a system like this they should have the Testing Tools to diagnose potential Problems.
About the only option you have available is to try the HDD in a USB Caddy. If you can get it to work there and not lock up the computer it should be possible to get at your Data though you'll probably need to Take Ownership of the Files by following the directions here
http://tinyurl.com/3aw7
However if you are unable to get the Drive to be readable and working your only alternative is to send it to a Data Recovery House to recover the Data on the Drive.
Col