i just replaced my mobo to a gigabyte 990fx ud3 and now system wont boot past the logo. resets, goes to startup repair, fails,

Boot from the windows installation disk - choose the option to repair the installation -- different MOBOs require different drivers for all of the components so trying to move a completed install from one MOBO to another will not work as it is trying to load all of the old drivers for the hardware that no longer exists - so you need to either completely reinstall or run a repair install that will force a reevaluation of the hardware and change the drivers it loads to ones that match the new hardware.