From: Ohio, USA
I occupied a previously unoccupied city and it has production power zero. Is it the case with all such cities?
If I understand your question correctly, what you need to do is set production for the city you captured. First click on the production button that has the factory pic on it. The city's current production will be shown. In the case of a newly captured city, the four production slots will be empty. You must select what you want each slot to produce. As long as the city is manned by your people type, you may produce anything that you have available to you, but if the city is manned by a different people type, you are limited to political points or resource production. In addition, make sure that you assign your city's production to the desired HQ, otherwise, it doesn't know where to deliver what it has produced.
Hope this helps... Happy Hunting!