2007 Hyundai Elantra Car will crank- but won't start

My wife has owned her Elantra since 32,000 miles. I take great care of all of my cars.
For some reason all of a sudden in the last 4 days, she turns the key and the car seems to have great difficulty starting it is cranking fine but no fire-up she has to perform turning the key 3-4 times cranking until the car finally starts.

Questions 1. What could be preventing the car from turning over?

Question 2. Would this work be under Hyundai's warranty to get it fixed?

Thanks, in advance for your help.

Steve