My disc has a white film or powder on it. Is it ruined?

Not necessarily, but it is a sign the disc is breaking down and should not wait. That whitish bloom is a chemical reaction in the coating that tends to get worse over time, and a disc in that state can become unplayable. Please do not try to clean it or play it yourself. Let me look at it first, because the wrong cleaning or stylus can finish off a fragile disc.