If you have installed / uninstalled it several times already you might have messed up registry entries. Run the uninstaller, delete the whole Muv-Luv folder and clean the registry.
If you haven't used registry editor before start it by writing regedit to your start menu search. Look for registry key HKEY_CURRENT_USER\Software\relic UGP Applications and delete that.
After this do a complete reinstall following the instructions. (Mount extra, run patch installer, mount unlimited, play).