leaking hot water tank

my tank is leaking bad.. we replaced the pressure valve twice still leaks, even with the water shut off to the tank it still leaks, ive drained it and everything,i shut the power off to it and the water supply to it got up next morning, water all over the floor! is it possible that we just bought bad pressure valves?? it heats water good, just the leaking is what is bad,please help!!! i even thought water pressure was it but it was not it