Unfortunately there is a problem with taking a hdd that has had a Windows operating system installed on one computer and then installing it on another computer. Windows recognizes certain identifiers from the motherboard chipset. When you start Windows it recognizes the identifiers and start the operating system. When you connect the hdd with another motherboard Windows will see the identifiers, when it goes to start it see the different identifiers and basically becomes confused and may not boot at all. If it does there is a very good chance that the operating system will eventually become inoperable because of the damage to the operating system.
In the future you should run sysprep prior to moving a hdd from one computer to another.
If you run sysprep on the hdd with Windows before moving it you should be be able to move it and boot from it on the other computer. You want to remove all hardware identifiers from the hdd, this generalizes the drive.
Click on the Start orb, then type cmd in the Search box.
cmd will appear under Programs above the search box, right click on it and choose Run as administrator.
This will open the Elevated Command Prompt.
In the Elevated Command Prompt type in CD C:\Windows\System32\Sysprep, then
use the command: "sysprep /generalize /oobe /shutdown"
Don't power the drive back on until it's in the other computer.
Note: You'll want to install matching chipset drivers, video drivers, etc.. after moving the drive.