If it's the same motherboard it will boot just fine, and you won't need to do anything.
If it's a similar motherboard, it may boot, but you should do a fresh install once you've backed up your data. This will eliminate possible driver conflicts, and general clutter.
If it's a different model motherboard, and it doesn't boot right away, do the windows repair. You can do this by booting off your OS disc, and follow this guide.http://pcsupport.about.com/od/toolsofthetrade/ss/windows-7-startup-repair.htm
Once the repair is done, you should be able to boot into windows normally. Then you should still backup your data, and do a fresh windows install.