If I understand correctly, you have an electric water heater.
The water heater is dual element and has 2 access panels on water heater.
You run out of hot water quickly.
And the reset is stuck down.
First of all, if the reset button is tripped, the water heater will produce NO hot water.
The reset, or ECO (electricity cut off), is designed to cut off all power to water heater.
So if you have some hot water, then ECO reset is fine.
The thermostat may be bad, but the ECO is fine
Next in line:
If your upper element is burned out, then the water heater will not make any hot water.
So if you have some hot water, that tells us the upper element is working.
The three remaining suspects are upper thermostat, lower thermostat, lower element
Let's test the lower element.
Turn off the power.
Remove both wires from lower element.
Test across both screws with a continuity tester.
The continuity tester has a battery and when light comes on, it says the circuit is complete.
Test1) Test across both screws on lower element with continuity tester.
If the light comes on then the element is good so far, but element has to pass one more test.
Test2) Test each screw on element to any bare metal part of water heater.
If the light does NOT come on with the second test, then element is good.
Element has to pass both tests. Light ON first test. Light OFF second test. Then element is probably good. This is not a fail-proof test but it is a good indicator.
I'm betting the lower element is burned out and you need to replace lower element. And you may need to vacuum out the sediment. http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
Now if lower element is good, then the easiest thing is to do is replace both thermostats. After replacing both thermostats, the water heater will probably work. If there is still a problem, then the lower element was not as good as the test showed, and it should be replaced also.http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html
If you are still having a problem, answer back and we'll give you more details.