Water started overflowing uncontrollably from the top of the water heater and streaming down the sides..what might be the problem?

The water heater needs to be replaced. The rust-colored slime indicates that the water heater has a leak.

Open the drain valve on bottom of tank

over heating possible bad gas control valve , relief valve bad or water pressure too high or overheating will cause it to leak also lack of thermal expansion tank

Copy following link for testing and replacing TP valve.
Do not cap off TP overflow tube, as this leakage signals problem.
http://waterheatertimer.org/How-to-replace-TP-valve.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

82V52-2 is typical 240Volt 50-gallon electric water heater.
Water heater has to be full of water before turning on power.
This is true for gas and electric water heater.

Once water pipes are connected, you are ready to fill tank.
Turn on cold water shut-off so water enters tank.
Open bathtub spigot on hot side.
When tank is full, water comes out of tub spout full stream.
Let the water run until there is no more air coming out.
Next, open TP lever on water heater for a moment, and this will bleed out last pocket of air.
TP valve is located on upper part of tank, on the side or on top. It is a brass valve with silver-colored lever. Lift lever for a moment and water will exit tank down the overflow tube.
Water heater is full.
Turn on 240Volt circuit breaker going to water heater.

Other links with electric water heater information:
http://waterheatertimer.org/How-to-replace-water-heater-drain-valve.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html#cleanelectric
http://waterheatertimer.org/How-it-works.html

No.
Water should not leak out of water heater.
Water should only come out of the TP valve and down the overflow pipe if water is too hot, or if TP valve is bad, or if you have stacking condition.
http://waterheatertimer.org/How-to-replace-TP-valve.html
http://waterheatertimer.org/Stacking.html
http://waterheatertimer.org/Leaking-water-heater.html

Is it coming out the releif valve on the side or top. If so it can be replaced, just shut water,power and drain down and replace.It is a standard 3/4" thread and not to costly.
Now it is the drain valve at the bottom turn everything off and drain it down and replace the drain valve.


Check out these links below for pictures and details to help you with this issue.
This link is for Pressure relief valve testing and replacement.
http://www.water-heater-repair-guide.com/waterheaterreliefvalve.html

The link below has an in depth details of how to change a drain valve out.
http://www.water-heater-repair-guide.com/waterheaterdrainvalve.html

There is 2 ways to do this.
The first way is to turn off the power. Turn off the incoming water (cold) to the heater. Go to a faucet close to the location. Turn off the cold water supply under the sink. Open the hot water side of the faucet. Allow any water to drain from the faucet. Make sure that the water coming out is not under pressure. You should be able to tell by how it come out. Easy, or forceful. Now go to the heater and open the bottom drain valve. The reason it does not drain very easy is because you have a vacuum. Similar to having a soda bottle full of water and turning it upside down. It will drain but it will "Glug" and drain slow. Opening the hot side of the faucet relieves the vacuum and it should drain o.k. When you are done with your repair, leave the hot side of the faucet open and turn on the incoming water to the heater on. Let it fill till you get a steady stream of water from the faucet. This "Burbs" all air out and ensures the tank is full prior to turning on the power. When you get the steady stream, turn off the faucet and restore power. In some cases, the heater may sweat because you are heating very cold water. This is normal and will only happen this one time.
Now if you want to know the second way, let me know. I've done it dozens of times with plenty of success and minimal mess.
Good Luck

could be pressure relife valve as well- you need to tell us where water is comig from exactly in order to solve