I did find the icon in the Tray. it has never launched to tray before. clicked it there and the UI opened. closed mirc and reopened and mirc opened normally. I don't see an option in Mirc to open minimized in tray.
re: the UAC the run-as-admin was not checked. I set it and loaded mirc got same UAC prompt. removed run-as-admin and still got the prompt. I might be misunderstanding. we could team viewer to poke around?