What model were the old and new motherboards?
Usually, windows will boot from the old os if they are similar enough. That allows you to load the new drivers from the new driver cd.
In the bios, there is a setting called sata mode. It will be AHCI, IDE, or raid.
It needs to match whatever your original motherboard setting was.
Try a different mode and see if your old hard drive will boot.
Usually, the only time I have a problem is when the motherboard changes from amd to intel.