Water heater will not work unless i push reset button will work for 24 hours or so then will stop working and i have to go out and reset it

The reset button or ECO (emergency cut-off) is a safety device.
The ECO trips and cuts off power to entire water heater when it detects temperatures over 150 degrees.
This prevents overheating and eventual explosion of water heater.

The ECO will trip for 4 possible reasons:
1) Bad thermostat. Water temperature inside tank exceeds 150 degrees F because thermostat is sticking in ON position, and thermostat does not turn off element correctly.
2) Loose wire inside or near upper thermostat that causes ECO to sense higher temperature
3) Bad element shorted to ground near center of element, and short does not cause breaker to trip
4) Factory-installed insulation and cover are removed from water heater >>> cooler air causes thermostat to read wrong temperature, and thermostat keeps heating water inside tank

Steps you can take:
First thing is to check if factory-insulation-and-cover are present.
Next look for signs of burning at or near screw terminals. Tighten loose wire if found.
Especially check the lower element screw terminals.
Take a photograph of the parts so you can see the parts larger on your computer, and compare parts more easily when buying new parts.
Next most likely suspect are the thermostats.
For around $22, you can buy generic upper-and-lower thermostats at Lowes or hardware store > then replace the thermostat(s) and see if problem persists.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

If problem continues after steps above
You will need to test water heater parts to track down the exact problem:
You need a inexpensive multimeter from Radio Shack, and the steps are simple, and you will know everything about an electric water heater afterward.
http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

Answer back if you encounter something not covered above, and I will help.