Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
If the old batteries have leaked brown corrosion onto things, cleaning will have to be done, of the battery compartment terminals at least, before the safe will have a chance of working again.
This is best done with cotton (or rag cloth) moistened with rubbing alcohol. Once the terminals are shiny again, let them dry for 5+ minutes, then put in the batteries - with proper orientation with regard to + and - poles ... and try the safe's combination again.
If at that point, lights don't appear on the keypad at all, then you either have at least one battery in the batteries you just put in, that is dead or is impeding the others (so change all for a completely new set of batteries, and completely new batteries too, in that case)... or else, otherwise, the safe is in that case 'broken'.