By licensing, if you have an OEM copy, its tied to the original motherboard. If its a retail copy its not tied to the hardware. If it is OEM often you can talk with MS, either they're cool and give you a code to activate or an option to purchase a new license at some fee. I've gone through both with installs I've done.
Option A. First make sure everything is backed up before any new hardware comes in to the equation. Run the install, it'll get you to the activaction point, then you may be prompted to call MS for a code. Call, step through the process and it'll likely transfer you to an actual human. Explain whats going on and see what options they give you.
Option B. Buying a new copy is in your future.