What movie is it ...?

I normally wouldn’t do this but i have searched IMDB for about an hour and have looked online, Theres a movie i saw one time about a man who gets trapped in what i think was a nuclear cellar for many years and one day the cellar becomes unjammed and he is able to enter the real world, and so on and so forth, i dont really recall who is in the movie or anything after that first part, i thought it was called back to the future but to my surprise it is not, so please help.