Hi Warren,
What is the exact meaning of 'won't open'? Do you get some error messages when you launch the application? This is weird after 2 weeks working normally. AFAIK, this has not been reported before.
The new installer packages are also uninstallers, so you should keep a copy of the installer file for the version you have installed, in order to uninstall it easily. With old 1.8.4 versions, the application distribution included an uninstall.exe executable, which is handier because the original package is not required. The software I am using now to generate installation packages on Windows (Advanced Installer) is great but does not support this feature, supposedly for good reasons (standalone uninstaller programs may cause problems with Windows in some cases).