I left my old job because I was a DON and I was working 80 to 90 hours 7 days a week.  We were so short staffed and the call offs were out of control that I never had a day off.  I had to fill all the vacant shifts.  When i go on interviews and they ask me why I left my old position. I tell that I could not keep up the pace of 90 plus hours a week and had no choice but resign.  I think this seems to turn them off.  I do not want to lie, however, telling the truth is not helping.  Should I make a reason why I resigned or is there a better way of telling the truth.  No person can keep working those hours and not crash.  Advice please.

No I am not telling them that I will not work extra hours.  Just that I worked 90 hours a week for months and saw no end to it.  To me if the company does not understand that a person can not be expected to work unsafe amount of hours then they are not worth working for.

 but everyone said that is a shortage in nursing, but they don't want to take any nurse, with or without experience! and the bedside nurses are burned out as well. It's a complete mess, don't you think?

You did well, because if you failed, because it's totally unsafe to work so many hours for so long: no safe for the patients, or for you and your license, when something wrong occurred because of that, nobody says that the nurse work a lot of hours and the provider does not have any strategy to prevent that! It's an administration problem more than your problem! It's totally unsafe for anyone!. 

Good luck!