Question
My orchid was left in the car overnight.  The flowers are lifeless and the leaves are thawing out, but how do I revive it?

Answer
From the sound of things, it was below freezing in the car overnight.  If that is true, the plant probably will not survive the frost.  If the leaves were frozen, they will become limp.  You didn't mention the type of orchid it was, but that may not matter if it got much below freezing.  The only hope for survival is if the tissue at the base of the plant(that gives rise to new growth) was not damaged.  You won't know for a month or more  if any new growth develops.  If the plant just got cold, but did not freeze, you have a much better chance of revival.