Bad Regulator or something else

hey folks need some help I have a kegarator and have had it for years noticed my beer stopped coming , nothing, ok checked and my pressure on the regulator was at zero, I assumed my tank was out of CO2, it was about due so I swapped the tank out w a new refilled one and hook it back up and still nothing, regulator reads zero, never had this problem before, is the regulator dead or something else, I know the tank is filled , no noise , no hissing and sadly no beer, I do not brew just buy kegs and yes there is beer in the keg. Any help would be great, let me know if you need more info Thanks