Did you make sure that the Power Cable was plugged in?
If it is boot the computer and enter BIOS this should involve pressing the [b]Delete Key[/b] or some other like [b]F1[/b] you will be shown the proper key to press on the bottom of the POST Screen.
Now make sure that you have both HDD's shown in the BIOS and depending on how old this system is you may need to Detect the HDD's or if it's newer they should appear in the first BIOS Screen which shows the Date & Time as well as attached devices. Make sure that both drives are present and exit BIOS saving the changes and allow the system to reboot.
Now provided that there is nothing wrong with the HDD when Windows opens you should see a [b]Found New Hardware[/b] message appear on the bottom right hand side of the screen and it will tell you when the HDD is installed and it may require a reboot depending on what if any software was loaded onto the D Drive.
Depending on when the Data Cable was pulled out the drive may need to be repaired as if the lead came out while it was running the Partition Information could have been corrupted but if the lead came out while the machine was turned off and being moved there should be no problem with the HDD and it's contents. If you can not read the drive but see it in the Disk Management running Check Disk on that drive may be enough to repair the Partition Information. but this only applies if you are running some form of Windows which you haven't mentioned.
The different forms of Windows require you to do this in different ways so I'll leave you to look up the Help Files on your system for the correct command to do this but you need to use the Repair Command so look up the Help files on your system and that will show you what is needed.
However if the lead came out with the HDD running the Repair Option on Check Disk may be insufficient and you may need to use some fully fledged Data Recovery Program like On Tracks EasyRecovery? Professional specs available here
http://tinyurl.com/kdeu
Or a cheaper option Spin Right a description is available here
http://preview.tinyurl.com/8p4ex
Lets know how you get on.
Col