Reinstalling the OS would probably be the best solution in the long run, but: If your current setup is either unstable or unbearably slow to safely get your valuables to another media (i.e. an external hard disk), in many cases you might be able to get a running system even without a reinstall. A regular surfer might not see any difference, whereas a heavy gamer might see some lack of performance.
The trick is to remove all the old motherboard devices. That can be done assisted by a Microsoft code in the Device Manager. I have compiled a small script to simplify the process, just copy and paste the three lines below to Notepad, save the file as 'devices.bat' and run it as an administrator. It will open the Device Manager with the opportunity to see non-present devices (=your old mobo) when you choose 'Show hidden devices' in the Options menu. Just remove everything that is greyed.
@echo off
devmgr_show_nonpresent_device s=1
start devmgmt.msc