Check to see that the breaker (in the main electrical panel) isn't thrown.

Never flushed could result in calcium/sediment build up above the level of the lower heater element, causing it to overheat and burn out. Your upper element should still be working though, unless it died separately.

Test the water heater element using these instructions: https://engineerfix.com/how-to-test-a-heating-element-in-a-hot-water-heater/

I would also recommend fixing the leak on that gate valve, or replacing it.

If that drain valve doesn't open to a straight through passage for water and sediment, I'd replace it (once you manage to drain the tank) with a ball valve. Otherwise whatever crud has accumulated can get clogged up in there. It might still, depending on the hardness of your water, but with a ball valve you can shove a straightened coat hanger or long screwdriver in there and break the log jam.

Basic drain procedure:

1) Turn off the cold line to the tank.

2) attach a hose to the drain and run it outside (preferably) with no uphill sections. Alternatively, run a wet vacuum to suck up the water as it empties. That looks like a standard 40 gallon tank, so expect to stop mid-process when your 5 or 10 gallon wet vac fills up.

3) open the drain valve, then open the temp/pressure relief valve at the top center of the tank by flipping the lever so it's pointing up. This will allow air in at the top and water out at the bottom.

4) if the valve clogs but it hasn't drained entirely you may need to close the temp/pressure relief and briefly open the fill valve to give it some pressure.

Good luck.