Well, you could reinstall Windows, but I guess you don“t really want to do that...

There is one 100% sure way to get SH3 running. Install VMWare Workstation, a virtual PC software (
http://www.vmware.com/). Create a virtual machine, install Windows, install "VMWare Tools", then SH3, then drag and drop the SH3 folder from your virtual machine to your real Windows.