You asked: 'thanks but does"when hell freezes over" make any sense?'
Yes, this is an idiom or saying. It is very emphatic, almost angry. It means "I won't let that happen!" or "That won't ever happen!"
"You say you don't like Schoenberg's music, but won't you consider coming with me to the concert?"
"I'll go to a Schoenberg concert when hell freezes over!"
Steve Jobs, the late CEO of Apple, was once asked whether Apple would ever develop any software for Windows. (Microsoft has developed software for the Mac). Jobs said "Apple develop Windows software? When hell freezes over!"
In medieval Christian theology, hell is a place in the afterlife where sinners go. In modern Christian theology, people who go to hell are excluded from communion with God. In medieval Christian theology, hell was depicted as a place of intense fire and burning "brimstone" (sulfur), and thus the ultimate in hot temperature. Since the fires of hell are said to burn forever, hell will never freeze over.