Shamelessly scraped from Tom's Hardware, posted by user PaperDoc:
You've run into a classic problem. You tried to use an existing installed version of Windows (on your HDD) on a different mobo, and that almost always cannot work. The reason is that EVERY Windows is customized when it is first Installed. The process takes a survey of all the hardware in the system and installs all the device drivers needed for it, but no others. If you then place that HDD in a different machine, you have some drivers installed with no such devices, and some drivers missing for the new devices.
There is a solution that works in many cases, but not all. You need your Windows Install CD for this. Place it in your optical drive and turn on, booting immediately into BIOS Setup. Go to the place where you specify the Boot Priority Sequence and make sure you have it set to boot from the optical drive first, and then the HDD. SAVE and Exit to boot from the CD.
Do NOT do a normal Install. Instead, find the option to do a Repair Install. This will do the survey of actual devices present now, then survey the drivers on the HDD. Then it will attempt to fix all the mismatches for you. When it is done, your machine may boot up cleanly, or at least with less problems. When done, remove the Install CD so it can boot from the HDD.
If you can get it to boot, go into Windows Device Manager and look for any yellow caution flags that tell you there is still a problem with a driver. You may have to solve those yourself.
Alternatively, bring up the system on the previous mobo, load the new chipset drivers, and then switch mobos.