You cannot count on windows.old as a backup. Best to back up your files externally.
With a mobo change, Windows 7 might start up but it is not assured with major hardware changes. If it won't startup then you can use Paragon Adaptive restore CD to boot and "Adjust hardware" which will remove all drivers
from Windows 7 so it auto-installs them at startup. Or you can Acronis 10+ with Universal Restore to back up an image which will remove all drivers before reimaging to HD.