I need some computer help!?

Hey guys, so I am swapping out my current MOBO which only supports things like intell corde 2 duo and quad. I want one that can support i7 and etc.. Also I am gonna get a new card but not really sure what to get? I currently have a 4870, but i was hioping for something better cuz i really want to play dirt 3 :P so my question is, qill changing my MOBO effect the data in the harddrive at all? Like will everything boot up like normal? or will i ahve to start from scratch again