Transfering Windows 7 hard disk to a new computer (PC, notebook, laptop) will cause OS not to start.
The most commonly used approach is to reinstall Windows and install all drivers and software on it. There are some cases where this is not preferred or will cause you much more throubles. So in this case we need to place Windows 7 in a special state, allowing the OS to boot with the new hardware/
This job could be done pretty good by a Windows application named SysPrep. It must be starter with rightclick and "Run as Administrator" on CMD.exe. Use this command to start it:
Do not start programs during execution of sysprep.
After it finishes, will will power off the computer. After that, you could add your new hardware or place the HDD to a new PC.
For full steps guide, read this article.