Sounds like one of your element thermostats is stuck. You have an upper and lower one. You can pick these up at your local hardware store. You can check these with a continuity tester but make sure you turn the power to it off first. If you don't have a tester you can disconnect power to the thermostats one at a time and see which one is stuck. Be careful not to short out the loose wires. As far as the leaking release valve, it should be ok after you get the temperature down where it belongs.
Answers & Comments
Turn the power off to the water now and have it serviced.
It is very important that you do the above.
This is a dangerous situation.
Sounds like one of your element thermostats is stuck. You have an upper and lower one. You can pick these up at your local hardware store. You can check these with a continuity tester but make sure you turn the power to it off first. If you don't have a tester you can disconnect power to the thermostats one at a time and see which one is stuck. Be careful not to short out the loose wires. As far as the leaking release valve, it should be ok after you get the temperature down where it belongs.