If your current operating system partition is intact, you shouldn't need to reinstall win7.
If you are using raid, you will need to duplicate the raid settings in your bios first.
If AHCI was previously enabled, make sure that it is set in bios.
If you want to do a clean win7 install, you might need to reactivate by contacting Microsoft by phone and simply explain your replacement motherboard setup. Just to be on the safe side, I would do a full backup of your existing boot partition using a Macrium Reflect free Linux or winPE dvd that you can create on another system. Macrium Reflect FREE Edition - Information and download
To avoid disk MBR problems, it's always best to install win7 (or win 8.x) with no other disk partitions connected and accessible until after the initial O/S installation has completed.