New mobo means you will have to reinstall windows. Different chipset (probably) and all sorts of other different hardware settings mean your previous windows is not able to run. My advice is to buy a new HDD and install windows to that, set it up and then connect the old HDD as a slave so you can get all your data back. When you boot to the new windows after installing the old HDD as slave, do it in safe mode and using explorer, navigate to the old drive and rename the windwows folder and reboot into normal mode. After securing all your old date use the old HDD as a data partition with all your data in a logical folder structure.