Plumbing Questions? Ask a Plumbing Expert.
Are you pressing the igniter repeatedly? It's difficult to see the spark through the viewing port
You could have a faulty igniter or possibly a clogged pilot burner orifice. You'll need to remove the burner chamber access panel. Once it's off you can see the spark (if any) better.
If you're following the instructions on the front of the tank (sounds like you are) and you're reluctant to remove the access panel then calling a plumber would be appropriate. BTW you don't have to turn off the water heater when there is a power failure.
There's no way a power failure would cause the tank to drain out.