Re-installation and de-activation

My old system disc was mostly corrupted and will not boot. On the same computer I have installed a new disc and re-installed Windows and Solidworks (2016). However, the license server of course still thinks the license is checked out to the old installation, and there seems to be no way to de-activate the license except via the installation that cannot run because the license is active. A classic catch-22. How do I de-activate the current license?

SolidworksGeneral