How can I get OBD codes in a car that won't start and has had the battery disconnected?

I have been working on a vehicle that had a check engine light, but will no longer start at all, during the process of trying to fix it I disconnected the battery, which reset the OBD codes. When I scan the computer it says no codes, I know there are codes, but I don't know if I can get them back without actually driving the vehicle and it currently won't start.