# Why did I come but there was no one there? Why did I call but no one answered?

"When I came to you, you should have been there, but you were not. When I called you, you should have answered, but you did not." or "When I came to speak to you, you did not respond to me."

# Was my hand too short to ransom you? Was there no power in me to rescue you?

"My hand was certainly not too short for me to ransom you, and I had the power to rescue you!" or "I certainly have the power to rescue you from your enemies." 

# Was my hand too short

"Was I not strong enough"

# Was there no power in me

"Did I not have the power"

# I make the rivers a desert

"I make the rivers as dry as a desert" 

# their fish die for lack of water and rot

"their fish die and rot for lack of water." The word "their" refers to the sea and the rivers.